Nothing can be done for low BP. Up salt intake and I drink isotonic sports drinks which makes me feel better.
It's actually quite normal for women to have low BP during pregnancy, if you have low BP I'd suggest getting some drinks (not energy drinks, just the sports ones) helps alot x
I don't think bad eating habits cause it, I lived on McDonald's at the start of preg with my daughter, and my low BP didn't happen till 17-18 weeks and I was healthy eating by then x