20 weeks

Im 20 weeks with second baby and have a doc app today at hospital, I been having horrible braxton hicks and just wandering if its worth telling them? I rang a week ago because it was actually that bad I had to take a bath, but they said its okay its normal just something is telling me something is wrong, I have a placenta previa and just so scared that something else is wrong, I havent been to a app since 18 weeks, is it in my head :( I had no problems with my first