Horrid stomach pains please help !?

My doctor prescribed me apo mefenamic awhile ago for my stomach pains. I take them the a few days before I get my period. I'm taking them since I'll be getting my period soon. But sometimes I just really immense stomach pains & I just feel like screaming. It's so bad I feel like my insides are churning. I'm also 16 if that helps anything. & the stomach pains last about 15 minutes then it goes away to a light bearable pain. & I can't even lay down. When I take the pills I can't lay down for 15 minutes. So what should I do ? Please help. What will help my stomach pains when I get them ? Something natural would help best or should I get new medication... & I'm not sexually active if that also helps. I don't know. Just tell me something !!