DS who is nearly 3 seems to be unusually sensitive. He's quite capable of being assertive and loud and demanding with his parents and has a reputation at nursery of being chatty, outgoing and friendly, but if another child tries to snatch a toy from him, or give him a shove, or shouts or says something mean he cries and cries.
Not unusual at all at 3 I think. He'll improves when he starts nursery and gets more used to interacting with peers. Keep taking him to parks and playdates and soft play and places where he has to learn to play and interact with others.