BP is eradic

Since I had liver cancer surgery my BP is all over the place. It will vary up and down as much as 30 points. The doctors have put me through all the tests and Echo but have no explanation. It acts contrary to the norm, I can monitor it after working out in the heat several hours and it's fine. Then I sit down for a few hours and it elevates. When I prepare for bed some nights it'll be high, I do a 3 minute light workout and it'll go back down to normal. It acts contrary to my activity and the doctors are stumped. If anyone is familiar with my situation and found a solution please let me know.