I am in the same boat. I’m 63, 5’9” and have always been thin with no stomach. I am now super thin at 114 pounds, but since going on meds, I have a bloated belly. It sounds the same as you describe yours. I keep thinking, between the antibiotics and probiotics, there’s a war going on in my gut. For the two years before going on the antibiotics, I was under a lot of stress, but this has only happened since starting the meds. Although I do want to say, as a health coach, I am always seeing stress turning into belly fat with clients. Particularly postmenopausal women.