I so feel your pain right now. I joined this site because I was getting a little stressed because I see there are others like you with my problems... I hope the best for you. My 3 day transfer was on Dec 2nd and the next two weeks are going to be the longest of the whole process...
i assume you are taking progesterone? if so then constipation and gas are totally normal (also can be caused by stress....which there is no shortage of when you go through IVF)
try not to over analyze every twinge as you will start to drive yourself crazy