I think it would be wise to seek out a professionals help here.
In my opinion, the behaviors you describe are not "typical", and since you mention starting a new school, her initial unhappiness, along with the urine episodes....I believe finding a really, good Child Psychologist could be very helpful.
I would do some research, talk to her pediatrician and ask for some referrals - then take her in for an evaluation.
From reading your entire post, I would urge you to seek out professional help NOW.
I am not a Dr., but a mom who has a child with mood issues, and have been proactive in her mental health care. When I read a post such as yours, it screams help.
Your son needs a professional. I would seek out the best Child/Adolescent Psychiatrist money can buy, and have him evaluated. I would guarantee this behavior will not just go away - I don't think you believe it will either.
After you find a really good Dr., then I would next focus on how to parent a child like this.
I have 3-"typical" children, then one who has been challenging since birth. Parenting my 4th daughter is a whole different ball game, and you'll need tips, guidance and support.
Here is a link to find a Child / Adolescent Psychiatrist in your area, and next is a helpful link for managing a child's behavior.
I have heard of a child doing this before - actually a friend of mine's daughter.
I think you are right to be concerned, and that's too bad the Dr. isn't really taking you serious.
This is a real issue, and is probably anxiety based - she is SO scared of choking, so scared that no matter what you say - it won't get her to eat.
I highly suggest you finding a really good "food therapist", or feeding therapist to work with your daughter. It may not be easy to find a "food therapist", but they are out there. Take your time, make phone calls, go talk to a center or a few Dr.s, then take your daughter in.
Here are a few links for you to get the idea of what you need to look for in your area.