Zantac Stomach Cramps, Stomach Pain, Ulcer Pain, Trapped Gas, Breathlessness

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.