Winniepig,
Please trust your instinct. You have written down the answer yourself, that you have noticed the change in yr child after the jab. The answer is obvious. Change of diet do not cause autism. Autism do not go away on its own. If a child do not have eye contact with their parents or do not respond, it is a cause for concern.
However, if a child is quiet but is able to express his needs through eye contact or body language. The child is slow in speech, just to need to communicate more to him/her. I know this because my daughter is slow in speech compared to other kids when she was young, but she responds when I call her. Now she is ten years old, she is able to communicate and socialize with her classmates. All children develop at different pace, but if they do not have eye contact with people or seems to be in their own world, it is not a normal behaviour.
There is a facebook group, Vaccines : A license to kill where parents share their story on how their healthy babies change overnight after vaccination. It is very heartbreaking for me to read how the kids change after a jab. Do read up on NVIC website if you have the time, as they hv been actively educating parents on the side effects of vaccination. Doctors in singapore or USA would never attribute these changes in a child to vaccination. There are parents like you who notice these changes after the child has a jab.
Winnie, do not blame yourself. It is not your fault. Is it confirmed that yr youngest child has autism? Does he responds to you when you call him? If the autism is mild, intervention will help a lot. I am unable to help you on intervention as I have no experience in it. There is a thread on autism in the forum where mummies shared how they help their kids. It Is at the discussion threads either at Motherhood, pregnancies threads or Matters of the heart thread. Do a search on autism and you should be able to find it. If you can't find it, let me know.