Some food sources of soluble fiber include oats and oat flour (mmm, oatmeal with peanut butter - my favorite!), carrots, citrus fruits, psyllium husk (like Lil was saying, it's a particular supplement). I'd just get a supplement but start out SLOW or you'll blow up like a balloon. Take a quarter of the recommended dose the first two days, then half, then three-quarters, then the full dose after about a week.
It will get better. Drink lots of water and get some yogurt too!