Overweight and weight gain :(

I started this pregnancy already overweight...well technically "obese" according to my BMI.
I was 186 when I got pregnant and 5'4''
Well, I've read that I should only gain 11-20 pounds and I'm 19 weeks and have already gained 8! I'm so worried and upset. 
I've been eating much better than I did before pregnancy and I walk 45min to an hour a day. I just don't get it. 
Any advice or words of support? :(