alex2kdl
Gidday mate, I have had a number of students with this problem, with a variety of reasons.
The most often is being too tense. As many here have said, you should be able to fly the 152 with your fingertips, even in turbulence. First try relaxing.
You mention its dam hard to trim out. When tense it is common for the controlling arm to either push or pull on the yoke. This is usually easily fixed. Try adjusting your seat position, it will often help, as it will free the arm aiding in comfort. I have encountered modified 152's that can adjust the rudder pedal position. If you can do this, then try that also.
This leads to, well, how big you are. Cessna 150's are small, if you are big then you wont be very comfortable, ergo, folding yourself half in order to fly is guaranteed to cause problems.
Madjock mentioned Carpal tunnel syndrome. I had an elderly student with this problem. It often affected him in other areas of life. In particular lifting heavy objects and using the likes of a computer keyboard. You have these issues? Even if not, it might be worth a visit to the quack. You can get support straps for the wrist (does hinder movement though) and an old boss of mine from my cooking days even went so far as to have an operation.
As for the engine misbehaving. Go see the mechanic. It will help relieve any worries at the very least.
Good luck.