I use the same program ...each muscle group once per week because i can concentrate all my efforts that day to one muscle group and that gives me better results ..
Until now I've only used Arimidex and it worked fine for me..Maybe for my next cycle i will use Aromasin because I see a lot of good reviews for this product from important members around here ,but i think that you should continue using Arimidex for this cycle if you started with it.
I had the same problem at my 2nd cycle .I had a cycle with testosterone phenylpropionate ,deca and Dbol as a kick start.After 4 weeks I removed Dbol and after that I didn't had any substantial gaines for the rest of the cycle.
I've used only Dbol at my first cycle,about 2 years ago, and i haven't lost much of the gains at that time,so i would recommend it to anyone ,especially for beginners.
For my first two cycles i used only arimidex ,but those where beginner cycles ,now i want to start the third with something stronger and i want some suggestions.