Androgenic hair loss is likely a hereditary condition. However it is not
given that if you had no loss prior to HRT, this trend will continue
after it. It all depends on the number of androgen receptors on your
scalp and how sensitive they will be to the increased androgen levels.
Unfortunately it looks like that the ARs in your scalp did not like all
this new testosterone.

)
However there may be a way to lessen the likelihood of hair loss while on
HRT. Application of topical spironolactone may be the solution. You can
obtain this solution from Dr. Lee in LA:
http://www.minoxidil.com
There may be other doctors who sell this type of a solution but
unfortunately I'm aware of any others.
Also there is some research that suggests Nizoral shampoo may have some
anti-androgenic activity. So you may want to wash your hair and scalp a
few times a week with this shampoo.
There is a theory (how valid this is, I'm not sure) that Nolva does very
little for gynocomastia. Some anecdotal evidence seems to support this.
Likewise anectodal evidence suggests that an anti-aromatose such as
Arimidex, Femara or Aromasin are far more effective in treating this
condition.
Another solution may be the topical application of a DHT cream.
As far as these drugs being safe or not in the long term, who knows???