Hi.. Can understand your concern.. As per your query stomach cramps and diarrhoea are the side effects of amoxicillin because amoxicillin is an antibiotic which kills harmful bacteria but along with this it also kills good bacteria present in human intestine... This causes upsetting of the intestinal functioning as the resistant bacteria left behind which are not killed by the antibiotics disturbs the normal functioning of the intestine leading to diarrhoea and stomach cramps.. These side effects mostly disappears as the antibiotic course is finished but if it does not happen you definitely need to see a doctor.. Till you are on antibiotics you should avoid milk products, high fibre foods and wheat containing food such as bread. Take plenty of fluids,fruit juices, soups, electrolytes so as to coverup the fluid and electrolyte loss due to diarrhoea.. You should immediately see a doctor if you have more that 5 to 6 heavy volume watery stools and severe stomach ache.. Any anti diarrhoea medicine should be taken only after consultation with a physician . Hope you get well soon.. Thanks and regards.. Dr.Honey Nandwani Arora..