Well, you can have words from me but wisdom is generally in short supply this end.

Have you tried letting your DS go to sleep in a bed with DH who then leaves? I know DS sleeps better if I'm in bed with him and I don't have to stay all night.

Can he talk well enough to communicate most things? Is he having nightmares and can tell you about them? You've recently gone back to work, how is the child care you have arranged? Maybe something there upsets him, can you ask? Maybe tell him a bedtime story where he does something and Spiderman comes to play/help him/rescue him related to these issues, point out that Spiderbed means Spiderman will be with him all night and that may help?

Best of luck, working and no sleep sucks.