Yeah, it's normal.
I gained a ton this way w pregnancy #1. Way more than necessary (45 lbs).
I recommend exercising (get out and take a walk) instead of, oh, maybe the halloween candy. Don't diet, definitely eat more, but, you know, try to cut out some of the crap if you can. I don't mean to be moralistic -- just if I had it to do over again (which I did, with #2) this is what I'd suggest.
And BTW, congratulations! You're in for a wild, awesome ride!
