I'm no gun tech by any stretch of the imagination, but I'm afraid you may be suffering from "worn out gun syndrome".
As you said, the gun is cheap. Things wear down, wear out, bend, and warp with use. For 50 dollars, a years worth of play isn't a bad life for it. I think the general rule for those is "use it 'till it breaks".
That being said, you can probably find someone here who may offer suggestions as to what you can do to correct the problem...but you also have to consider if you really want to be shelling out for replacement parts on a budget gun.
Always expect the worst. That way, you're never disappointed.