A SERM like nolva or ralox will be more effective at reversing gyno than an AI will but first you must make sure it's gyno. The lump behind the nipple would feel different than the fat in the area bc of a different density. Sore nips don't mean gyno but if you actually do feel lumps that's gyno
Nolva at 20mg daily or ralox at 30mg daily until gone. May take a while but those are your best options not including surgery b
Raloxifene is the most effective treatment for gyno (along with getting estrogen levels under control via some sort of AI). Nuking estrogen with letro to reverse gyno is stupid & outdated.
Ralox has been shown in studies to be more effective than tamoxifene at reversing gyno (one specific study looked at pubertal gyno that had been present for a significant period of time). I have personally used raloxifene to reverse developing gyno more than once. 30mg is not enough. Minimum 60mg/day preferably 120mg/day for at least a little while, then you can drop down to 60mg/day. ReliableRX, ADC, ClearSky Pharmacy all sell raloxifene (evista). Some research companies do too, but I can't encourage you to buy that research stuff.
Also, EVERYONE has some sort of little lump behind their nipples. You may not need a SERM right now & might be able to take care of the issue with just an AI.