I have put 6 liters of oil inthe truck in the last 2 months. Its not leaking out and not visibly buring the oil either. The truck runs good and doesn't seem to be affected by this. i just cant figure out where all the oil is going.

There are many possibilities for finding oil on the oil pan. The easiest way to determine where the leak originates.

Step 1. Steam clean the engine
Step 2. Add an oil dye to the engine.
Step 3. Drive/run the engine for 30 minutes.
Step 4. Check to see if oil is visible on the pan.
Step 5. If visible, then with the florescence light see where the oil is coming from.
Step 6. If not visible, return to step 3.

oil change period is every 6 months or 5000 miles or 10000klms
however as the oil collects moisture from incomplete combustion any short runs that do not allow the engine to come to full operating temperature to boil off the moisture will need a more regular oil change
So if the car does runs of at least 1/2 hour the the 6 months will be ok
On the other hand if it is only used to go around the corner to a corner shop then more frequent oil changes will be required
Good policy is oil filter with the oil every 6 months or if more frequent with every second oil change

4 liters in 6 month is abnormal, usual cause of oil loss is worn out piston rings, your car need piston ring replacement

burn oil check market for release piston rings.

Mobil 1 is really thin,if you have as oil consumption
problem ,run a thicker oil,10-30 in the winter 15-40 in the summer
Suspect valve seals,not a cheap fix ,but a little oil burning makes the
engine last forever,run a thicker oil.

The front seal on the AC compressor is very likely the problem here. It can leak with no apparent signs of leaking like older R12 systems because the oil used in the R134 system is synthetic and it evaporates.

Either the oil leak isn't from the filter seal and is somewhere nearby or the oil pressure is unnaturally high, perhaps because the oil pressure relief valve is stuck closed.

Sorry old school dinasaur here ,no 5000/6000 miles a service ,sorry for being hard but that is my service schedule it also includes changing wheels around including the spare .Topping up battery ? oiling door hinges checking everything and oiling nuts on suspension so they dont go rusty ,spraying underneath with waste engine oil to prevent corrosion ,drilling a drain hole in boot if its not draining .cleaning light bulbs and greasing the buld contacts .maybe drill a hole in outside front floor pans if windscreen rubber is leaking .Think i should go get back in my coffin now before i get told off .

If you have no visible signs of oil leaking out of the engine then the oil is being burnt. By visible leaking I mean a small puddle of oil under the car after having been left overnight. This can be cured by replacing shaft seals and gaskets. Burning oil is visible as smoke under deceleration (no throttle) and under full power(flooring it). This is due to worn/old valve stem seals(smoke under deceleration) and worn oil rings(smoke under acceleration) This can only be cured by a major engine overhaul or engine replacement. Bear in mind that losing a pint of oil in 1000 miles is acceptable.

How many miles/km's you drive in those 3 month's ? oil consumption is normal ! Check when you first start the engine in the morning wetter or not you see a puff of blue smoke, if you see smoke , your valve seals are leaking.
1 liter oil each 2000km is normal.