After four days on this medication my husband experienced a bad u...

After four days on this medication my husband experienced a bad upset stomach and lost a lot of blood when he would use the toilet. He now has headaches, sunburn, and grinds his teeth at night. He was very short tempered and lost interest in food. Normally he looks forward to meals. Now all he wants to do is eat sweets especially dairy products which he normally does not eat such as ice cream. This seems like a lot to put up with just for an infected tooth. Can someone please explain some of this as it is very frightening especially the blood.