constipation medicine

I'm 6 weeks pregnant and my first appointment isn't until July 19. I recently had problem with my digestive system almost 2.5-3 months ago and they recommended me taking some sort of laxitive. 
I know some things aren't good for the baby though. 
Since mt first appointment isn't until a couple weeks out and I'm having problems again. Can anyone recommend a OTC medicine that's pregnancy safe?
I tried eating healthier. I drink 6-8 glasses of water a day, I exercise, I eat plums. 
I don't know what else to do. This makes me so nervous that it's harming the baby since I can't go. Please help!