Zantac and stomach pain

Have been taking zantac 300 for about two weeks. At the beginning, took it in the mornings but fatigue was so extreme that I had to switch to taking it at night. Started waking with extreme breathlessness and stomach cramps, which I didn't tie in with the tablets. Two weeks later, stomach cramps (stomach and centre abdomen) are getting increasingly worse. I've also had increased anxiety, a trapped gas feeling in entire abdomen, I burp constantly but the burps don't relieve me and I feel breathless and very panicky with them and I also feel that I am full up to my eyeballs, even after the smallest amount of food. I've lost my appetite even more (something I didn't think was possible considering how little I was eating). My joints and muscles ache. But the reason I'm going to stop taking this tonight is the unbearable stomach pain, I'm hoping the Zantac is the reason for this ... the ulcer pain that I had prior to starting Zantac was more bearable, I think I'll stick to antacids.

I have a 9 month old baby. At the age of 2 weeks he started having a lot of stomach problems which included constipation, colics, vomiting, blooding. After several medical examination it was found he had acid reflux and allergic to regular baby formula. He was placed a special formula called Nutramigen. At the age of 5 months we have noticed him to be very hyper, won't sleep much even during the night. During the day he might sleep twice a day (app. 9:30 a.m. and 4:00 p.m.) for maybe 45 minutes at the most. He wakes up twice a night when before he was sleeping for almost over 8 hours. Like I said this happened at 5 months old. He is on Zantac twice a day. Could this medication be affecting him in this manner. He at times looks quite tired, stays still for a little while and it seems like he recharges and gets more energy. This is also taking a toll on me as I don't get too much rest and the interrupted sleep at night is affecting me. Please let me know anything that you can on this situation or who or where you can refer me to for more research. I feel something is going on with this medication.

Extreme stomach pain, especially when eating after being hungry.