I was given a rubella vax just after my son was born. I then nursed him for months. He since has been diagnosed with autism. Connection?

No. There is no connection between vaccines and autism. There is misinformation from many people about this, including from some non-medical hollywood celebrities. The one researcher who claimed this initially later admitted he falsified the results.
No. The alleged connection between vaccinations and autism in the same individual has been thoroughly discredited. Although antibodies are present in breast milk (on of its advantages over formula), that is a passive phenomenon, not something that would set off any type of reaction in your son's body. We don't know the cause(s) of autism, but this is not one of them.
No. You may want to have your son screened with newly available genetic screening tests. Recent advances in understanding the genetic code have been very revealing. They have developed ways to look for misinformation spliced into the gene code with markers.The suspect the majority of autism sufferers have such abnormalities.When found, the represent changes present in egg or sperm before conception.