low on vitamin D

i have been low on vitamin D since I was like 10 weeks pregnant i am now 21 weeks and I'm still low. I've taking my prenatal and my vitamin D pill every day and it hasn't went up in 2 months. So my doctor told me to keep taking it and they will recheck it in a month and go from there. is this something than can cause harm to my baby? I'm starting to get myself worked up about it. I never had this issue with my other pregnancies! I just a peace of mind over this!