27 weeks and gaining too much?

Today I am 27w 2d, I just got my glucose test and am waiting on results but I've gained 38lb so far this pregnancy and I am very nervous about that. I don't want to be unhealthy or cause complications but I eat healthy the majority of the time and stay active but have no idea where this weight is coming from and where it's going?! I mean my belly is big but my little man has been measuring 2-3 weeks ahead since the beginning and the doctor comments on him being a big boy but he's surely not all of that weight. I lost 15 lbs in my first trimester and then around week 20 I POPPED and grew a ton and now I'm 38 lbs past my pre-pregnancy weight and I'm very freaked out. My doctor is setting me up with a nutritionist to test my metobolic rate and see if we can figure out where it's coming from but I just feel like I'm failing. It's really making me feel horrible and I don't know what to do. I've been told you can hardly tell I'm even pregnant from behind but when people see my belly I've gotten a few "are you sure it's just one?" or "man he's going to be 12lbs at this rate". Anyone else in my boat?