Is there a problem with me only pooping every 2 to 3 days, and does this lead to fat gain?

For some: A bm every 2 to 3 days is normal. It should not cause a weight problem

Bowel movement : No every one has there own bowel schedule from multiple times per day to once a week or even less often If the stool is not hard or painful it is ok It does not lead to fat gain

Don't Fear the Fat: Probably not. That's not outside the realm of normal as long as you feel OK and don't have to strain too much or if not a lot comes out ( in this case a 'bird' in the hand is NOT worth two in the bush, or three, etc)It may lead to some weight gain as you gather more 'birds', but not fat per se. Then after those 'birds' have 'flown away' your weight will decrease accordingly. But don't fear the fat

Not always but...: Having BM's every 2-3 days may not be terrible but it's optimal to have daily BM's; otherwise toxins in the stool can be reabsorbed. Of greater concern is the cause; chronic constipation can be caused by hypothyroidism, insufficient dietary fiber &/or fluid intake, lack of exercise, magnesium deficiency, lead toxicity, intestinal yeast overgrowth, imbalances of GI flora etc. See a doc to evaluate.