Do not mix AIs, you will compound your situation. Letro is an AI. AIs should be used on cyle to keep e2 within range and prevent gyno from ever being an issue. AIs will not reverse gyno. For gyno treatment you need either ralox, nolva or surgery. It would be a good idea to read the attached thread below.
Stop Using Aromatase Inhibitors to Reverse gynecomastia! SERM's Only! You should have a hormone panel that includes sensitive e2 and PRL in order to find out exactly what's going on inside. 25mg/day of stane is the dose I would normally recommenced when using 500mg/week of test. It's not possible for aromatase to build up a tolerance to AIs. Unless you use pharma grade AIs then there always the possibility that you received bunk or under dosed product.