Allergy to Anti Biotic

Patient: According to my doctor I must take anti-biotics for 7 days. I have taken them for 4 days, but due to lots of stomach problems, I want to stop taking them. All the time I have a feeling of vomitting and I have lost my appetite. I am taking 2 tablets of Co-trimoxazole 400 each 12 hours. Means 4 tabs a day