Hello Bungo
I understand that eating a lot of plant food can lower blood pressure so perhaps your diet, meds and now HRT have combined to bring if down further.
I eat a whole foods, plant based now but my blood pressure has always been on the low side. A GP once asked me if I ever felt faint and when I said no, he said I didn't have a problem. A visit to your GP is a good idea and your BP meds may need to be reduced.
Take care.
K.