It's not just while you're doing school or homework that you can get uncomfortable. Playing video games or handheld games or using your cellphone can all cause discomfort if you sit or lie in one position for too long. If you were in your lounge and there was a couch, a beanbag and a mat, what are some comfortable positions you could find to play your games or use your cellphone?
The most important thing is that you keep changing your position before you get uncomfortable. Don't just stay in one position for a long time.
Remember that if you stay in one position for too long, it won't hurt the first time you do it, but you'll feel discomfort and pain over time.