Im 5ft 11in im 21 and 130pounds i can't seem to eat and when i do a poptart will fill me up for hours, i don't understand why?

Doctor can evaluate: For feeling full shortly into a meal, there are many common reasons. The primary care doctor, after one or a few visits, can evaluate for the common causes. A patient can make a symptom diary, writing down on a calendar the foods eaten. Some causes are gastritis, acid reflux, gall bladder problems, etc... A gastro-intestinal specialist can do added testing if needed, or if cancer is suspected.

Fat: Diet is everything. Look at the fat gms on a poptart. Weightlifters who want to lean out will eat 5 small meals a day;in between meals if they get hungry they will eat a handful of nuts which are high in fat. Try 5 small meals a day for 2 weeks 400 cal each and low in fat.