I went to a Developmental Ped at a Children's hospital for my son's diagnosis. A regular ped can't diagnosis they really don't know. They are like a GP for an adult, physicals,coughs, colds, etc..... The OT should be able to give you an idea as to what is going on, feel her out and see what she says, express your feelings as to what you have researched, if she does not agree then get a little bit more assertive. What other SPD tendencies does he have: smells, sounds, touch, textures, sensory seeking, etc.... what other things do you see at home and when you are out. Does he have a hard time transitioning from one thing to another.
I think you made a good choice homeschooling him while you figure things out ( or forever! ), but the social interaction is very important and I am sure you are aware of all the awesome homeschooling groups and activities. I homeschooled my older son for 1/2 of 1st grade but my SPD child would not allow it so that was the end of it! lol He was very demanding in the beginning, but he has come a long way!!!!! So things will be fine once you get the information you need to find your way to help your son everything will be ok.
I have never given my son meds, so I don't know about any of that and he doesn't have the other issues. Good luck, stand your ground , don't be intimidated, and if you do not feel he connects with this OT try another. Remember after some sessions he will be even more out of whack but will transition eventually. Keep us posted and drop a line anytime!!!!! Good luck again!!!!!!