Breast Reduction - Breasts Get Bigger 2 Weeks Post Op?

Always  best to check with your own plastic surgeon about concerns after surgery. Online consultants will not be able to provide you with meaningful diagnosis, treatment recommendations, or reassurance.
Best wishes;  hopefully, you will be very pleased with the  long-term outcome of the breast reduction procedure.

Swelling reaches a crescendo 72 hours after surgery. If you are premenstrual now, then this could certainly account for swelling but you should be seeing your plastic surgeon in followup such that seromata, hematoma, infection, etc can be ruled out. Additionally, you should not overdo activities two weeks after surgery.

The breast are changing and settling into position and may appear to have changed size.  If you feel any hardness that wasn't there before, or they are gradually enlarging then I would definitely contact your surgeon to have him or her evaluate your breasts to make sure that there is nothing going on besides normal post-operative swelling and changes.