I have apetite for 3weeks now, and wen i force myself to eat i get a running tummy then i feel weak after that ?

Get checked: Three weeks is a long time to have these symptoms and I feel they warrant a visit to the physician for evaluation. Possibilities include gastritis, irritable bowel syndrome,viral infection, food poisoning or intolerance. I assume recent foreign travel and pregnancy are not issues. Until examined, eat a bland, nonfatty diet containing no harsh roughage. Take kaopectate to control diarrhea. See MD