help with bloating?

It's not period related, well it gets worse when I'm on my period but it's basically all the time. I have been bloated for like a month now maybe longer, it feels like there's air in my stomach and it's painful. It's actually starting to hurt my back. You'd think I was pregnant but I'm not. My belly sticks out and everything, my period isn't due for another 8 days. I've been to a doctor and he told me it was just gas, and I am gassy too so I mean there's that. Could it be my diet? Like a gluten allergy? Also what can I take to help really relieve it? I took tums and pepto but it really didn't do much. My doctor told me to do that.