it could be the hCG. As it is a hormone.. this could be your bodies reaction to it. Not saying it is an allergic reaction persay, but strictly - it is a H.O.R.M.O.N.E. :) Will it go away?! Everyone is different, so there is no concrete "yes or no".. Might be there while you adjust to hCG... or after it leaves your system.
or it could be TOM, though i'm not sure when that is. i know that sounds weird but the birth control i'm on causes me to not have TOM, though i still get the cranky, bloaty, wanna eat everything in site stuff. and the occasional breakout