Vagina pain..

I'll be 33 weeks Thursday and been experiencing horrible vaginal pain, it gets worse when I lay down and nothing helps. My doctor thought it was due to an infection and prescribed me a one time pill and said it should give me some type of relief within 2 days.. itll be 4 days tomorrow and I still can barely sleep due to the pain. Anytime I try to move it hurts way too much down there, any idea what it could be.? I didn't experience this with my first.