Two year old won't wear shoes!! Desperate!

My two year old son, diagnosed recently with ASD won't wear his shoes. He hasn't been able to wear shoes for two months. He won't put his feet on the floor and cries hysterically. I've tried putting him in the same design of shoe - didn't work. It's like he's in so much pain... He withdraws into himself and becomes very subdued. This can last for a few days. I'm struggling. I need him to run and jump around outside in the fresh air to encourage him to sleep at night. ANY suggestion would be so welcome. Thank you so much for reading.