A Workout Question: rollerblading -- why is my butt getting bigger?

I’ve been rollerblading for a while now (about a month) about 3 times a week. In the beginning of my workouts it was always a very quick fix; I’d work out and 2 days later I would see my butt get drastically smaller. I’m 150 lbs, female, not fat but not skinny either.

So that was in then. But I noticed as I kept doing it (particularly, now) I’ve reached a point where my butt is actually getting BIGGER. I’ve talked to some people who say it might be that after this frequency and prolonged period of blading, the muscles started to develop under the fat and are pushing the fat out. Should I keep at it, hoping that the muscles will bust the fat or should I worry that THIS is what I’ll get from blading (an even bigger butt)? I really, really enjoy it as a sport and I feel great doing it.

I’ve had a similar effect before doing targetted butt workouts (like lunges and that kind of crap) where my butt swelled up for a few days and then melted away magically. So what do you guys think (fitness people)?

Also, I did not drink enough water after and before my workouts and I am trying to do that now to make sure it’s not water retention.