Pain under right breast

The last couple of weeks I've had this tingling sensation occasionally usually at night. It didn't hurt at all just a weird feeling. The last couple of days it has turned into pain. I'm 20 weeks so I'm not sure what the problem is. Some times a heating pad helps considerably. I'm not sure how big the baby is to know if it's just the baby getting bigger or my ribs expanding. I'm on vacation and worried it could be something with my gallbladder but can't call my doctor where I am. Anyone else have this?