S.,
My son is in the process now (has been for the past year) of being evaluated and treated for SPD, PDD, etc. He is now 5 and overall we have seen great progess, it seems to be 2 steps forward, one step back. I completely understand how difficult, trying, scary, and isolating this all can be.
First off, I found the SID-DSI all about kids Yahoo group to be a wonderful lifeline of support, suggestions, and approaches. It gave me hope and help. Major help. I never would have found some things we needed w/o it.
We will not give our child the flu shot either. It contains MSG (which is a soy derivative, and just figured out my son is allergic to soy), formaldehyde, and mercury. You can do some research and get a medical/religious exemption. I'll home school my kid before he gets a flu shot.
You will need to read everything you can about approaches to autism/spd. PDD is Pervasive Developmental Disorder and is the medical term for autism.
If you try to get help through the schools they tend to do the bare minimum that is legally required and it usually doesn't make a dent in what your child needs. The school systems are overwhelmed with special needs kids. Get what you can from the school, then figure out what your health insurance covers, if anything, and then decide which therapies you feel are worth fitting into your budget. We have just come to accept that there IS NO extra money. Anything that does not pay bills goes to therapies. We have tried many, many things. In our experience we had great results with some alternative things that no one has ever heard of, but if it works and is safe, that is all I care about.
See if there is an Easter Seals facility or an autism specialist center somewhere in your area and get on the waiting list. Your son's diagnosis should by law, make him eligible as a child with a disibility for medical assistance to help cover his bills. If they haven't already, the school should have a social worker spend some time with you to help you navigate the systems to get your child help.
There is no right or wrong way to live with/handle this. It is trial by fire and you do the best you can, get help where you can, pray hard, and take care of yourself so YOU can be strong for your kids.
I bring this up because I see that your youngest has multiple food allergies. Food allergies and sensitivities often contribute to PDD/SPD symptoms. Most MD's and allergists will tell you that is not so, but many, many moms have seen differently and now some MD's (DAN (Defeat Autism Now)-doctors), and most homeopathic or naturopathic doctors agree and know how to biomedically help your child go into a sort of "remission". Many, many PDD/SPD parents strictly follow a glutein free, casein free, soy free diet - it is a pain at first, it takes awhile to get your family's diet and grocery habits all changed around, but they do it because sometimes the results are THAT dramatic. Pulling my son off of soy has shown me that. I use a NAET practitioner to find out my son's food sensitivities because it is painless and easy.
Research,research, research, read, ask around, talk to people. Email with moms around the country to find out things you can try to handle it all. Take care of you.
L.