Son with spd?

I have a 21 month old son who has always been the kid that chews on everything. It doesn't matter what it is, he just has to have something in his mouth. The other day I found some plastic that he had chewed and I never did find the rest that was missing. He chews on shoes, toys, blankets, table's anything he can get to. He also eats quite a bit and has had problems with eating because he sticks too much in his mouth at once. Im not sure if he has SPD but would like to get opinions before talking to Doctor. Any information would be helpful. Thank you