I've had somewhat the same experience. I quit smoking 3 months ago and started eating a whole lot more than I used to. I'm little too, and skinny (or I was, I've gained about 5-8 lbs. since I quit smoking). Anyway, I felt the same - terrible constipated, gassy, bloated, disgusting - hungry too, all the time, but stuffed! uuggghh.
I started taking fibercon tablets (I'm only 30) but that really helped out tremendously. I took 2 a day for 3 days and drank lots of water (because you're supposed to with those) and then waited, things got better after a couple days and within a week I felt back to normal (meaning normal before I quit smoking). Strangely, not as hungry either. Try it, maybe it will help a little.