Dark spot in scar, what could it be?

Thank you Janegrace for posting your question here,I will start by stating that my answer is based on the limited information provided, for a more bespoke plan please consult with your plastic surgeon.
I am sorry to hear that you had to go through multiple drainage procedures, though uncommon , hematomas can occur, I hope you feel better soon.
When it comes to dark spots within the nipple scar it can be a number of things and it is hard to assess without examining you or at least looking at pictures. Just by virtue of their location and assuming that they are small in size , if I had to guess it could be a suture granuloma, or a suture that is yet to be absorbed that is trying to make its way out , that being said , I cannot definitively advise you on the matter without an exam .
I hope this helps, best of luck!

It’s not possible for me to give you meaningful input to your concerns without having at least a visualization with a photo. That said, the reactions of the tissues after a hematoma as well as the potential additional issues with sutures in the incision and how they could be affected by a hematoma that was drained three times, make this an issue which your plastic surgeon needs to evaluate as soon as possible. Best wishes.