Cool that's listed as a potential 5-AR inhibitor -
https://www.ncbi.nlm.nih.gov/pubmed/16093232.
How much were you taking, and for what reason?
The 5-AR is an enzyme converting T to the more potent and androgenic DHT. Excess DHT is unhealthy but some is needed for men to be men, if the astaxanthin was effectively killing it then it switched your body , or at least your breast, into estrogen dominance, and that explains the gynoid flare, but this is rather speculative.
Ditch the aromasin or any other AI stick to SERMs when dealing with gyno. Try taking some creatine to get your DHT up again.