Is The sentence "I think my boss is OVERWORKING IT at the moment" correct? No, that's not right, sorry. "work" is the action that is being done - so "over working" would be the problem. "it" in this case is also work, so your sentence is saying, "over working work" it doesn't say what you want to say. To, "work something" is to operate something, "work an action pump, to manually pump water" - so you can over work (operate too much) the mechanical pump, but you can't over work or operate your work/job/duties of employment. So choose from overworking, or over doing it. I hope that helps.

Overdoing it brings a different image to my mind. It might mean decorating for a party, and overdoing it or going inappropriately "too far" with her decorating ideas. You can get dressed up and overdo it. It means being inappropriate....going too far. When you work too hard or too long, you can definitely be overworked and frazzled. She needs a holiday or a vacation. So a boss can be overworked, and needs to take a break and rest up. That sounds right.

You can say: "I think my boss is overworked or "I think that my boss has been overdoing it"