What causes lower back pain right above the buttocks started on the left side day 1 and 2 day 5 worst when rising sitting mim when standing?

It's sciatic nerve pain. I know. I get it all the time, and it drives me bananas. Once I sit down, I can't get back up again, and lying down is worse. Try using a heating pad on it, bengay and Tylenol. It will pass in about a week.