I've just gone up to 25 mg of Zoloft, and my stomach is a mess also. It should be a temporary side effect that goes away as your body adjusts to the medication. I take Pepto when it gets bad. It's unpleasant, but I prefer to go through this temporary discomfort than live with the awful anxiety!
I had the same reaction as you. Remember there is usually a temporary increase in anxiety when a dosage is increased. The increased anxiety can cause more stomach acid and therefore your symptoms. I confess I take omeprazole for the heartburn. The burping went away with the anxiety. My stomach burned so bad I thought I had an ulcer. You can get prevacid or prilosec over the counter. Either one should help. Good luck and excuse yourself!