The sulfur burps I am not sure if there is a correlation or not but could be gerd/acid reflux. Before my surgery in 2007 I had chronic acid reflux for a year. I came off the meds the day before my surgery and it never came back. I had adhesions on my stomach and it was pulling it out of place so that for me was why it was causing that problem.
As for the diarrhea, does it happen the day before your period? Like everything comes out, then the next few days constipations/bloating/pain and then a bowel movement sometime during that week then the pain subsides?
If this is the case or it sounds familiar I had bowel and rectovaginal Endometriosis. Mine was cyclic but I also had rectal pain throughout the month at random times. The day before my period I would evacuate my bowels completely and I knew that wasn't normal for me because I have had supposed "IBS" since I was 15 and was always constipated.
Bowel endo is also misdiagnosed a good majority of the time as IBS.
Your period can definitely aggravate gastritis or GERD. Hormones can mess with the sphincter that keeps the acid down in the stomach where it belongs. If you know it is coming, maybe you could take some Gaviscon (available over the counter) to try and keep it down? I use it - it keeps a layer on the top of your stomach acid and really helps me. Liquid works better than the tablets.
Have you also had your gallbladder checked?
I also forgot to mention just, structurally, bloating can push everything upward too... if you can try and treat the bloating, that might help too.