Had a colonoscopy two days ago and ever since then I have been feeling really weak and tired? Is this normal? Also legs have been feeling restless?

That is unusual. Typically colonoscopy does not cause any such problems. It is possible you had too much of a bowel prep activity(?Severe diarrhea) which can cause dehyderation or electrolyte imbalance. Please hyderate your self with lots of lquids and a pinch of extra salt in your food or drink lots of soups or electrolyte solutions for a couple of days, then you should be fine. Do inform your doctor who did colo.