L.S.
One thing you might try as well is to use Grandma one day a week as a treat. I know he is very young, but maybe you can say - if you can be good this week (no hitting/biting/etc). you can stay with grandma one day. Maybe you could even start small - if he is good on Monday, he can go to Grandma's on Tuesday. Then, expand it - if he is good on Monday and Tuesday, he can go to Grandma's on Wednesdays.
I 2nd another mom too - with the sensory overload. My son had sensory integration disorder and his behavior at daycare was very different from home. At home, all was organized and quiet and he could get my undivided attention at any time. But at daycare, there is a lot of noise and a lot of other kids. My son spent a lot of time crying just from sensory overload.
Good luck!
L.