Booly, I'm sorry the Doctors don't have an answer for you yet, I'm sure this is frustrating and scary. Are you able to walk without fainting or getting dizzy? Do they think it is weight related? Gosh I hope you find out soon why your blood pressure is dropping. I'm guessing you are monitoring at home too is there a pattern to when it drops such as when you get up or if you exercise strenuously or does your BP remaking the same sitting, standing, and lying on your back?
You are still early in your post op are you getting enough fluids and protein?
I wish I could help more. I'll say a prayer for a speedy resolution to your heart problem.
Best wishes
Kt