Kathryn , I agree with others. An antibiotic doesn't 100% fit everybody's body. There are oodles of them out there, which will work & not cause the discomfort you're experiencing. A call to the Dr. would solve this. It's worth a try anyway.
When my Gastritis is acting up, & when it was absolutely intolerable, I had the Dr.'s diagnosis, he gave me tips & advice to follow, & I went on-line. I did a search on "Gastritis Diet." It helps to eat/drink these foods, so you don't have acid, gas in the stomach, GERD, pain in the upper belly & it cuts down on the feeling of vomiting or vomiting. Sorry, if it's TMI.
The diet consists of "some" things, as no coffee, no tea, no chocolate, spicy foods, fried foods, no pops, and there are things, which are good. Like poultry, fish, broiled, not fried. Almond butter is good. PB & margarine AND butter are O-U-T! Almonds are good for it. Something in the almonds help coat the stomach, making it feel much better, you get in protein, & you can buy them in bulk, too. I stayed away from eggs, because of the gas. I had broiled foods, canned foods, & frozen. I seemed to be able to tolerate those microwavable dinners just fine. I stopped using margarine on bread or toast, but used Almond Butter instead. Since I couldn't have butter or margarine on potatoes or rice, I use a sprinkle butter called Molly McButter. Rice is very good for this, too, especially for settling down the stomach & for protein.
I know the diet sounds absolutely terrible! But it sure worked/works for me. I use GasEx after meals & at bedtime. I'm feeling so much better. Yes, I "DO" have those days when.... I'll have something I shouldn't have had, or if I get stressed, I can have a "flare", but it goes away quickly & I'm my old self within a few hours, if I follow those Gastritis Diet guidelines.
I think that antibiotic you're on is the culprit, so I hope you'll be able to get onto a different one, which is much easier on your poor tummy. When people have "things" like this pop up into their lives, it affects everything, because we all need to eat food and/or drink, too. I certainly can sympathize with you. We ALL want to be able to eat, drink, & be merry, digest our food & feel good after we consume our meals & snacks. I wish you the very best. I hope you can get back to normal very soon. I hate seeing you suffer with this. You sounds strong, like you're a real trooper, you've been through so much in the past, health wise, too. I know you can & will get better & see some light at the end of the tunnel, too. Just wanted to let you know, I've been thinking of you, & will say some prayers, too.
Good Luck!
I hope it's a super Satisfyin' Saturday, for you & Everybody here today, too! 
That's super news about the FitBit walking neighborhood group, too! 
It seems like daily- it's always "something" or 1 thing, doesn't it? 
