Really bad stomach gas...?

To fully understand, we need to go back to where this all started: In April, I got my cartilage on my ear peirced, a week after getting it the peircing site got very infected, and the infection spread to my jaw and face. I was in and out of the hospital with fevers, allergic reactions to antibiotics, etc for about a week. I was put on 2 pill antibiotcs: Doxycycline and Septra DS, I was also given a rocephin shot. 3 days after being on these medications I experianced some bad side effects and allergic reactions, I was taken off of the pills and put on a strong dosage Keflex, while on ALL of these antibiotics, including Keflex, I have had really bad gas and constipation. I finished the Keflex about 5 days ago but still am experiancing gas. It is in my upper stomach and gets SO bad that I cant even get up and move around. I tried drinking ginger ale to help relieve some a little and it doesnt help. Also, I am on Nexium for heart burn but havnt been taking it because I feel my heart burn has been under control. Is gas a side effect of heart burn and are these antibiotics the reason I have gas? What can I do to help get my digestive system back to normal?? Any advice?