Studies have shown bio-identical estrogen to be favorable to blood pressure, more so if taken non-orally as it is a vasodilator and increases nitric oxide. Non bio-identical estrogen such as conjugated estrogens and ethinyl estradiol can have a negative effect on blood pressure, as can some progestins like medroxyprogesterone acetate (Provera) and perhaps cyproterone acetate (Androcur).
Spironolactone as well as bio-identical progesterone (Prometrium, Utrogestan, Cyclogest), albeit to a lesser extent, tend to lower blood pressure.
This is what I gathered from studies, so far. I'm no expert though.
Are you stressed since starting HRT? With any change, we tend to be a little more stressed. Also, was your blood pressure measured at a certain moment in time when you were particularly stressed/anxious? Was it restested in different conditions, like at home, a second and third time at doctor's office, etc?
I do hope your doctor took all the above into account. Keep us posted and good luck.