How To Take Low BP Pills If I Have Tachycardia?

I have Tachycardia, half of a thyroid, IBS, Endometrosis, and going through Menopause. My Tachycardia scares me all the time and i have low blood pressure which makes it very hard for me to take the blood pressure pill they want me to take. I feel jittery all the time in my chest and i always thought that might be A-Fib or thyroid but my Internist doesn t seem worried. I am 53 years old and have exercised all my life -i am having a hard time exercising..Don t know if i should blow off my Internist and go to UAB because it makes me think and feel like i might die at a young age.