Blood Pressure 79/58, Extremely dizzy, 34 weeks pregnant?

I've been feeling really dizzy here lately especially today, im super tired, and have a head ache. i took my blood pressure and it was 79/58, im 20 years old and my prepregnancy weight was 120. I also have a heart condition and i take Metoprolol tart 50mg a day, this medicine is also used to treat high blood pressure so it lowers yours, my blood pressure before i started this medicine was always in the 90's/60's but now runs in the 70's/50's i'm waiting for my doctor to call me back but is this to low for pregnancy or in general?