Most likely, thats what we call estrogen rebound. Its not totally uncommon. I'd suggest letrozole at 2.5mg/ed for atleast 7 days. I would also continue at 1mg/ed for the next week or two. Go by how you feel and the progression of the lump.
Warning: This will most likely effect your sex drive. A small amount of estrogen is needed to maintain a good sex drive, and the letrozole is gonna totally wipe out all the estrogen you have. You should return to normal a wk or two after stopping the letro. Consider getting some cialis.
Good luck bro, gyno can be a bitch.
Chris