I'm anemic and always been small
It's okay as long as the baby is gaining and growing, my Mom was diabetic on many pills for it and high BP she thought it was menopause at 43 and was 3months pregnant when she found out, to control her diabetes and BP she was put on a well balanced diet ate very healthy and like 35lbs the doctor wasn't worried at all because my little sister was growing and weighing fine. She was born healthy with no complications :D
I'm 32 wks and I have gained one pound and at my 30wk ultrasound baby was over 4lbs. If your doctors aren't concerned then I'm sure your fine. Every pregnancy is different and some women don't gain a lot of weighy
I am one who never gains more then 10 to 12 lbs during pregnancy and I'm on my 4th. My doctors have always told me as long as the baby ks growing and gaining then there is no need to worry. I'm currently 22 weeks and I've only gained 7 lbs so far. But if you're really worried talk to your doctor. I hope this helps.
Were you sick in the beginning of your pregnancy? If so then your body could just be making up for lost weight. If you're really concerned it doesn't hurt to talk to your dr. I hope this helps.
If your doctor isn't concerned then it should be okay, but maybe other moms can give you a better explanation because I didn't have this problem.