If you only gained 2lbs over 3 days it could be anything...remember scales measure EVERYTHING in your body, not just fat.
As an example: I went down to 116.6 and then back up to 119.5 recently. It WAS disconcerting, but I KNEW it could not be fat because I would have had to consume thousands of extra calories over my needs into order to put on fat, which I didn't do. I looked into my nutrition record on Fitday and realized I was low-carbing (not on purpose) and then began to eat lots of carbs again right before my weight jumped. Well, when your body replenishes its glycogen stores, it also stores more water, which can result in a "magic" 3 lbs or more gain! Sucks, but it's helpful to know the facts and not get discouraged.
Remember, if you are tracking everything, and you know you aren't taking in more calories than you are burning, then it's physiologically impossible (barring other medical complications) to gain fat.
Hang in there