C.L.
Sounds like my son! He's almost 3 now and it has gotten better, but he's now lapsed back into screaming/crying when I leave or my husband leave him with anyone.
What we did was avoid any large groups and things that were overstimulating and focused on small playdates or groups that were less overwhelming for him.
If he sees social situations as a fun experience then they'll continue to get better for him.
He has gotten much better with age. We took him to a Tiger game at around 18 months and I ended up walking around with him for about 30 minutes or more and he just wouldn't calm down so we left.