S.,
Welcome to the world of atypical developmental disorders!
First and foremost, you cannot let these hurdles of doctors not knowing what to tell you and insurance denials be road blocks. Dust yourself off, and pick yourself up, it may happen again and again before you think you really know what to call your son's condition, you may never have a name to call it.
We have been there, and you just have to move on to the next doctor until you find an answer that makes sense to you. You will know when you find it. Refuse to be a victim of insurance, schools, doctors, etc. Untie your hands and move on to do what your son needs right now, what ever that may be for today...
We have had the best luck, far and away, with Developmental Pediatricians. They will act as a case manager for you also and will make referals for his entire program. It may take a while to get in to see one, but make an appointment and put yourself on thier waiting list for cancelations, and call every week to see if you can get in sooner.
If your insurance will not cover speech, you must find a way to pay for it yourself. You will probably end up doing this alot, it is a sad fact for children with developmental disablities. It is not fair, but it is what it is. Even once he is in school, the public school is NOT obligated to give him as much speech therapy as he needs to reach his full potential, they do not have to help him maximize ANY potential to its fullest, they only have to offer him access to a basic floor of opportunity. Find a therapist, get him weekly speech therapy, and do the homework dilligently to make your dollar go as far as it will go. The sooner you start, the better the outcome.
Explore sign langauge, it will help him with his frustration. Find some simple signs on the internet and start using them yourself, he will pick them up too and once he can comunicate, he may be less destructive. Another tip that I got from a preschool special ed teacher for our nonverbal daughter was to tell her what I wanted her to do instead of what to stop doing. They are not at a developmental stage where they can flip what you say and do the oposite, it really does help them.
If the Ritalin helps him, use it. It is one of the most tested medications there is. Drug therapy for the symptoms children with developmental issues suffer (and the DO SUFFER) can be releived effectively with medication. There is absolutly no credible evidence that any of the diets, suplements, or other "cures" work, but if you choose to try them, do not abandon standard therapy. Any one anecdotal story about someone whose child improved with these things is not helpful to you at all, so try not to listen to anything other than double blind, repeatable studies done by repuatable researchers. Your son does not have time to waste on false hope, and although traditional treatment will not offer you flashy results or cures, your son will make real progress which you will learn to value in time.
Therapy, medication, and special education will have a measurable impact on his condition, no matter what the diagnosis turns out to be. Emotional disorders, toruettes, ADHD, ASD (autistic spectrim disorder) etc, all have the same treatment protocal, you treat the symptoms that you see and you offer theraputic interventions and educational solutions to target specific needs.
Call the county MRDD board and find out what evaluations you need to have to get him on their lists, do what ever it takes, if the lack of diagnosis is a problem, try to get him a diagnosis that will quailfy him, even if you have to change it later, and you probably will anyway. Once he qualifies and has a case worker he will be eligible for respit service; they will send a qualified care giver to your home for several hours a week to give you a break. You will need this. He can have a "noncategorical" lable once he enters the public school system at age 3 until he reaches school aged service (grade 1) and this may be enough for MRDD. Check with them and get the process started.
I wish you the best, it is a hard road. You did nothing wrong, sometimes it just happens. I would also suggest that you ask your doctor to test him for Fragile X syndrome, this is one of the possible disorders that could be ruled in or out with a blood test.
M.