What Causes Muscle Twitching In The Diaphragm During Pregnancy?

I am 22 years old, 116lbs, and currently 24 weeks pregnant. For some reason I keep having these muscle twitches around my diaphram area. It is not fetal movement as no baby is that high near my breast at that young. They don't hurt, just feel weird. I have been having pains before and after meals in which the OB said about taking Pepsid to relieve, this doesn't work. I'm wondering what could be going on. I will be talking to him about this next week.