Hi M., I am not a professional, nor do I have a child on the spectrum or dx with anything beyond maybe strep throat from time to time.
I worked at a special needs pre-school for many years. I worked with many (many many) parents who were profoundly convinced diet was a HUGE factor, or the ONLY factor, or vaccinations were a HUGE or ONLY factor in their child's Diagnosis. I certainly could not disagree with them. As dramatically different as each child on the spectrum was, each child's PARENTS were very MORE diverse.
I found all the children I worked with fascinating and even MORE loveable than my own boring normal children (I know that sounds awful), I was always on line researching, bought a zillion books, could not WAIT to get to work to see what kind of day I would have with which child was my one on one.....I did not always agree with our schools policies, procedures, behavioral plans which started to wear on me more and more.
One year for Christmas, my guy bought me the book 'Ten Things Every Child With Autism Wishes You Knew', by Ellen Notbohm.
I had already read so many books written by docs and pros, this one was entirely different. Written by a mom with a child on the spectrum. I found it LIFE changing, I LOVED her philosophies, SO very different from the philosophies at my school.
Anyway, I shot my mouth off one too many times....disagreeing with the 'pros' who came up with the plans for my one on one (who was NOT showing improvement or progress of any kind, and who I loved like my own, and was convinced I knew the route to take with him, sigh). So I got fired! All I could think about was Oh My God, what's gonna happen to this poor child!
Anyway again, try everything, read everything, talk to everyone, eventually you will form your own opinions and theories and THAT'S what you go with for your own child.
Good luck, it's a very rich life with a child with these dxs, read the Ellen Notbohm book even if your child is entirely different than hers, and enjoy him!