L.M.
Hi K.,
Whoever is watching him while you are at work is not exhausting him enough...lol. I would ask them to do more active things with him. Also, I would take him directly to a park when you pick him up. It may be the last thing you want to do when you are done working, but that hour in the fresh air will tire him out and give you some sanity.
This may sound rude of me, but hubby needs to step up - even if he gives you 30 minutes a day playing with your son. That is not much to ask of him, and that will give you a much needed break and keep you sane.
I also try to stay in the moment. I try not to look forward to what needs to be done. Sometimes, that is exhausting in itself.
Good luck and hang in there,
L.