I can sympathize with you on this. My grandfather was in the hospital recently (got out several weeks ago) but while he was there, it was hectic dealing with the doctors. But I found that the problem usually wasn't with the doctors but rather with the nurses, as they would tell the doctor something that's complete nonsense and the doctor has faith in their nurses. So it's understandable when they continue on this incorrect path. When the patient and the family inform the doctor of the opposite occurring, then the doctor is left to decide who to believe, the nurses who he/she has worked with for a while or the random patient and their family.

However, a doctor hitting a patient is inexcusable. Writing no diagnosis and discharging the patient when the patient clearly is ill (i.e. vomiting) is also inexcusable. Some doctors are stuck-up because they have a M.D. and the patient and their family don't. You could either simply go on with life and try to get a different doctor or you could get a different doctor and file a complaint.

If you bring him back to the same hospital, then they're probably going to see he was in very recently. You may be able to get a different doctor and get it all sorted out. That happened to my family a few times, one doctor I thought was good but later on realized he wasn't and we had to rush my father (mind you we had to call the fire department because he's well over 320 lbs, wasn't sure where he was so you had to somehow try to restrain a man over 6ft3, over 320 lbs who is incredibly strong. After we got the fire department and paramedics over, we brought him back to the same hospital and demanded (I won't try to write the entire dialogue as it was fairly long and didn't have the nicest of words). Anyways, we got a different doctor and lo' and behold, that doctor was pretty fast on the diagnosis, gave him a few pills and said in about a week he should be fine. In 4 days he was completely better.