No pressure in clutch pedal until pumped 12-15 times..then shifts fine...next day same thing pedal goes to floor and then gets pressure after pumped 12-15 times

see if this link helps you find out why.
2004 cavalier clutch pedal goes to floor Google Search

Replace the clutch master cylinder and clutch slave cylinder as you have a failure in the system allowing air in and that is why the pedal goes to the floor and will not return up. May be a proper bleed of the system first may fix the problem so do that first but if the fault comes back after a few days then it will be dollars time.

no fluid in the clutch reservoir due to a failed clutch slave cylinder
time to replace both the clutch slave and master cylinder

on the transmission there is a slave cylinder that works like a brake cylinder, when you apply pressure to the clutch pedal a rod inside the vehicle under the dash pushes into a clutch master cylinder, (almost like a brake master cylinder without the reservoir, as the clutch master cylinder works off the brake master cylinders reservoir) the plunger in the clutch master cylinder applies fluid pressure to the slave cylinder,(located down on the trans near the clutch fork assembly) which projects a piston rod into the clutch fork dis-engaging the clutch. To bleed the clutch slave cylinder locate the bleeder screw on the slave cylinder,break loose so it loosens and tightens easily. Check fluid in brake master cylinder reservoir,fill if needed, while bleeder on the slave cyl is closed have a helper push clutch pedal to floor and back 7-8 times, (At first the clutch might stay at the floor, just pull it up by hand or foot and continue) after several pumps with no rest time push pedal to the floor and hold down with foot pressure, at this time loosen the bleeder on slave untill fluid leaks out, watch for air bubbles, close bleeder and repeat untill there is no sign of air bubbles, (make sure to check fluid in the brake master cylinder and keep fill as needed, do not let fluid get less than 1/2 empty as it might **** air and you will have to start over) If this does not bring clutch to operate then you need to check if slave cylinder is reachig its full extension of push rod or not. If it is not then you will have to replace the clutch master cyl or the clutch slave cyl or both as seals are bad and wont hold pressure. Or you need to inspect the clutch fork,the throw-out bearing, or the pressure plate fingers and clutch plate for failure or broken bent parts. I hope it turns out to be a easy fix on that clutching thing.

It is likely you have drawn air into the system. Check the clutch reservoir and refill if needed. Use DOT 3 or 4 brake fluid. Bleed the system to restore clutch pedal. Check the clutch slave cylinder for leaks. If leaking, the slave cylinder will need to be replaced and the system bled again. Please let me know if you have questions.

if u know u have every thing hooked back up the way u took it apart then i would rebleed the system that should do it.

I believe your pressure plate is broken and at a minimum will have to be replaced along with the clutch disk.

It is most likely a hydraulic clutch, and it is most likely leaking at the clutch slave cylinder. Check the clutch master cylinder for fluid, it should be a small master cylinder looking thing with a fill cap next to the brake master cylinder and booster unit. If it is empty fill it with the same dot 3 brake fluid that you use for your brake master cylinder, and make sure that you are pouring the fluid into the clutch master cylinder reservoir and not the rubber seal that should be under the fill cap. After filling the clutch master cylinder up with fluid, then try and pump up the clutch pedal. It might take a while to pump up hydraulic pressure, and you might also have to work the pedal a few times by hand at first.

Also, you might have to bleed the clutch at the slave cylinder if it will not build up enough pressure to release the clutch.

Sometimes the slave cylinder takes a little extra bleeding to remove the air in it & until it's all gone, the clutch won't open completely, causing the problem you are describing.

If the shifting can be done between all of the gears while the engine isn't running on level ground then the forks should be ok & not bent inside the transmission and you should be able to get the car to shift properly.

I've done several of these and found that if you start by making sure the Clutch Master cylinder is full, and remember when you add fluid, try to add without aerating the fluid. Pouring down the side of a funnel is better than pouring straight into the container as fluid picks up air during the splash. Hopefully doing it this way will prevent small new air bubbles from getting back into the lines when bleeding.

Next, after having one person pump the clutch pedal quickly 3 or 4 times & continuing to hold the pedal to the floor until you've completed this phase, instead of just releasing the pressure through the bleeder valve, also push on the clutch fork/rod to go ahead & force the fluid completely out of the slave cylinder, tighten the bleeder and have the assistant slowly pump the pedal to bring the slave cylinder back into contact to where it was before you pushed it to drain it. Refill & bleed as usual a couple of times. If you don't have a good clutch pedal now with good release, you need to check the Clutch Master Cyliinder since once the bleeding is done, this is a completely automatically adjusting system. good luck

ok every time you open the clutch resevoir you have to bleed the slave ..next hold down the clutch to the floor open the bleeder screw 10 mm bolt and then close it and pick the pedal up off the floor if your clutch is not right the pressure plate is failing most likely on mitstu stuff ...bleed first ..