breast/rib pain

So I've been having some bad pains under my right breast sorta like around my rib cage. At first I thought it was from my bras so I do not wear wired bras but the pain still comes. I asked my OB and she said it could just be muscle pain but it honestly feels way worst than a stretched muscle. It started as a random come and go thing but now it's becoming more consistent. Anyone have any idea what this could be? I'm 19wks with twins.