AC not working & blowing out hot air.

What is your question?

I have a Mazda 3 2006 and I bought the car used from a dealership last December. The car was fine until the summer time came around. When my car gets very hot because of outside temperatures the AC started giving me problems since last year, only months after I bought the car. Last year we went to autozone and put sealant/refrigerant oil in the car. It seemed to have fixed it last year but now I am having the same problem again but worse. The AC can be turned up as high as it can go and the air is still warm or barely cool. If I sit in the car while parked the AC will start blowing hot air or the car will stall. If I drive the car after it has been parked while the AC is on then the air starts to turn cold again again, but only if I am driving around. Just a couple days ago I had a friend try to put sealant/refrigerant oil in the car again and it wouldn't take it. He said it was backing the hose out. Now the AC is blowing only warm to hot air. I'm not sure what is wrong with it but I was told by him that it might be the clutch. I think he was referring to the compressor clutch but I'm not sure if that is the real problem. Does anyone have any suggestion to what it might be? I am hoping it is not expensive because my husband is deployed and money is really tight and I won't be able to afford anything really expensive. Lastly, the antifreeze/coolant reservior is full and I have not really seen the fluid deplete from it so could that also be an issue as well?