General question from parent with child (ASD)?

I understand there are many different behaviors/symptoms of ASD and it's not that cut and dry. My son has ASD, his main areas of concern are sensory issues such as, speech, gross/fine motor skills and arm flapping/stimming(which is at least moderate, sometimes really severe/the stimming) . He is only mildly socially unaware, not insensitive, likes to engage and smile, sounds and lights don't bother him, however certain clothes do. I am looking for a parent that has a child with the same symptoms or maybe not. I would like advice and guidance on the things you may do that I am not currently doing. I know a lot of parents find food allergies/vitamins and other care besides pt, ot, speech. What are these vitamins and what are the main food allergies you find?. I will say that he has been in some form of ot and speech for 3+ years and I don't feel like his progression is as good as it should be, because there were times I would take him 5 hours week for these visits. Any advice? Any break through therapy or holistic things you do at home? Just newly informed to this and what to make all the appropriate and best decisions for his welfare.