Your weight gain seems fine to me, pretty similar to a lot of us here. Every woman, and every pregnancy, seems to be different - the nurse at my second-last OB appointment said every woman has 'her time' to gain weight. For some, it's early on, for others it's in second or early third trimester.
I've been up and down all through my pregnancy -- my pre-preg weight was 143 (BMI was 23), but I lost about 10lbs right at the start, then gained it back and by 22 weeks I'd put on an additional 15lbs. Since then I've lost a few pounds, and at 25 weeks my weight seems steady at 156lbs; a gain of 13lbs over my pre-pregnancy weight.
I think as long as you're eating fairly well and feeling good, that's what counts. Whether we like it or not, we're going to put on 20-40lbs (or maybe more), but it's for the best cause possible. I'm having a bit of trouble adjusting, and need constant reassurance from my hubby and best friend that I'm not a hideous whale, but they've actually said as my belly grows, my face & legs look thinner if anything. My hubby says I'm gorgeous, so I'm trying to focus on that and not the numbers!