It take me weeks to have a bowel movement, and when i do either it's very hard or it's diarrhea. and it smell like burnt plastic. what could be wrong?

Eat more fibers: Commonest cause of constipation like yours is that there might not be enough fibers in your diet. Try to eat more fruits, vegetables, and salads. If need be you can also get something like Metamucil or citrucei from pharmacy or supermarket and take it. If the problem still persists then you should see a family doctor or gastroenterologist.