Looking for answers

(Indiana)

My son will be 5 in November. I have always worried that he may have autism but my mother in law, who is an OT says there is no way. He is a very sweet little guy. He engages with other kids and plays, he's learning at a normal rate, he loves to interact with his younger siblings...someone from the outside would never think anything different about him....however, ever since he was able to crawl, he would rock back and forth in the crawling position.

Today is continues to rock (VERY hard) when he is awakened at night, he turns his head back and forth (very hard) in his car seat while we're driving, he loves rocking in our recliner for long periods of time. He also has a love for fingernails and toenails. He will rub your nail (with his hands and/or feet) and grab at the edge of the nail, also. He will do this to anyone who will let him. He also sucks on his tongue when he's tired or feels anxious. He gets tense and flaps his arms when excited about something. He has also withheld his bowel movements since 18 months old and we're still dealing with that today.

Lastly, he has a hard time following commands. You have to tell him multiple times to do something before he seems to understand. He has a hard time playing sports because he never knows what he is supposed to be doing. I've always just called these his little "quirky" behaviors and reading through other stories on here, I've read the work quirky from other parents. I'm just trying to figure out if any or all of these are SPD related and what in the world is my next step?

I'm just so fearful of him getting into school and being made fun of and therefore having a low self esteem. I want to help him and also figure out if these are just quirks, or if there is a name to put with them. Thank you for any suggestions you may have!!!!