My question is: Did you get a lot of gunk out with your colonics? If so, it is possible that you now absorb your food better than before (which is a good thing I'd say), and what the body doesn't need or cannot use it stores away of course (e.g. as fat).
I am personally pretty much underweight due to bad absorbtion, and with cleaning my colon I hope to get to a proper weight again. I really eat A LOT now (always hungry), but I don't gain weight at all... which is a bad sign.
I don't know what else could cause it. Fluid retention? Maybe someone else here has other explanations.