Hi welcome to H.C.M.Forum. the blood to the chair has nothing to do with the gastritis
or the drugs you have used. it could be due to hard stools as a result of the drugs, or due to internal piles. for gastritis besides the drugs you have to maintain the food pattern. avoid spices, chillies, sour foods, junk foods. avoid irregular food timings. eat more of curd and bland foods. thank you.