I would find a new one. You need a doctor who considers ALL possibilities when you bring your child in with an illness...Someone who does tests "just to be sure" it isn't something else. And who can put aside past experiences with other children and not assume that just because your child has some of the same symptoms as them, that they have the same issue.
Now...finding a Doctor like that is rare! I bring my son to the same pediatrician for all of his well-child visits, but when he has any other problems I bring him to a different Dr almost every time. That way if he did have something like a UTI and one Dr says it is a stomach virus, and I take him home and am not convinced, I can see another Dr for another opinion without having to argue to the original doctor that he must be wrong.
One thing that did happen to my son was during birth, his collarbone was broken. No one knew about it until he had a chest x-ray 7 weeks later and found out that it was already healed. Well, I believe now the broken collarbone also caused his torticollis...my son would always keep his head turned to one side no matter what I did [I tried wedging him in the other direction when he was sleeping, trying to get him to turn it all day long, etc], and I am convinced that this was because it was painful for him to use the other broken side. Since he always wanted his head turned to the one side, he developed plagiocephaly [flat head on one side]. I told my son's Doctor about my concerns when my son was FOUR months. He said "why don't you come back in a month or so and we will see if it has gotten any better". I didn't like that answer, but I didn't see another Doctor at that time for a second opinion because I trusted him. Well, I took him back around 5 months, and at that point he said he would refer me to Gillette Children's Specialty Healthcare to talk to a specialist and see if he needed a Craniocap to correct it. So, I scheduled the soonest appointment available [2 weeks out] and yep, he needed physical therapy and a Craniocap. BUT...it took another month to get in for the imaging of his head, and another couple of weeks before the Craniocap arrived. My son was over SEVEN months old before he got the Cap. I found out that the most effective time to correct his head was between 4 and 6 months!!!! We used the Craniocap for a few months and went to physical therapy...but since we started so late, his head is still not quite normal and he is 16 months. There's no going back. Anyway, I feel so dumb for trusting that Doctor. I didn't feel right but I didn't seek another Doctors opinion. Never again!
So you can see why I think you should switch, and any time you think the Doctor might be wrong... or especially in your case when you KNOW the Dr was wrong, see another one! Your child's health is in YOUR hands