My AC will not cool

My ac unit is not cooloing like it is suppose to. I recently changed the liquid lines on the van and got it to cool very good for about a month. After family got back from florida I notice the air was starting to not get as cold as it did. I checked pressure on the low side of the line and it was up around 90 to 100 psi. I know this pressure is to high for my system. It should be around 25 to 45 psi. So bled the the lines down and I noticed that there was barely any freon oil coming out but alot of air came out and the air was not cold. I put in two 12 ounce cans of 134a into system and the pressure went back up to the 90 to 100 psi again. Is this normal? The air in the cabin of car was still not cold but the rear air vents was alittle cooler than the front vent which was not cold at all. My questios are why does the pressure register so high, why does the rear vent blow cooler than the front which does not blow cold at all. My van has the rear condenser and seperate blower fan, and the compressor clutch is activating. Thanks