At 22.5 wks I've gained 11.5 lbs and had a 20.7 BMI pre pg (like you), and I'm just about the enter the phase where baby picks up 6-8oz of her own weight each week. I've noticed a lot bigger daily increases in the last few days, and I'm guessing it's just par for the course. I do have friends who are the exact same gestation as you and have gained 25+ lbs, but they also started out slim, and I have no doubt they'll lose post partum. One of my good friends was very tall and slim and gained 50+ lbs with her baby this March, and she's losing it very quickly. She said she worked out w/ a personal trainer 4x/wk. It is my belief that those who start slim or workout during pg do gain more--it does set you up for adequate stores for BF, and baby has his/her needs.
I just try to focus on getting the good, healthy foods I need first, and if I have room for the treats, I eat those next--and try not to worry if it gives me an extra half pound a week. I know this awesome eating ride is going to come to an end after birth (I was eating 1500 calories/day, running 3.5 miles 3x/wk and avoiding all kinds of desserts, alcohol, etc--it's not the funnest existence), so I'm enjoying having a higher metabolism while I still can!
Muffin, 2010
Bubba, 2013
"You've probably heard the expression 'I believe in God, just not organized religion.' I don't think people would say that if the church truly lived like we are called to live. The expression would change to 'I can't deny what the church does, but I don't believe in their God.' At least then they'd address their rejection of God rather than use the church as a scapegoat." Francis Chan