How low is low blood pressure?

I've been on Lisinopril 20mg for a week now. I have been having the hoarseness, leg cramps, tired (no energy), getting no sleep, and cough. But what worries me most is my blood pressure has dropped to what I think is TO LOW, (example: 87/60, 90/58, 96/66 89/68. I called my dr. 2 days ago and explained my concerns. They told me to cut my 20mg pill in half and we will decide what to do at my next appt. which is in a few days. Even after cutting the pill in half, my bp is still running 96/67, 98/66. Should I demand to be taken off the Lisinopril and be put on a different medication?