Thank you everyone. I can't tell you how glad I am you guys cared enough to help me and I hope you have more tips for me.
As for the the lesson tonight, I went to it and I warmed up as usual and my back wasn't that bad in the walk and trot. At first it hurt to post but then it felt better after a few times around. While cantering I did a circle and every time he placed his front feet on the ground my back hurt so bad. Then it would release and as soon as he took another stride it hurt again. So I told my instructor and she said let's just try a little more and tell me when it hurts. So I did that and she said let's see if you can jump a little crossrail. So I finally convinced my self to do it and I was nervous of course. He jumped fine but he jumped a little early and there was agonizing pain in my back. When I told her she said try again and follow him all the way through. He didn't hurt as bad then but it still wasn't enjoyable. During this my riding partner was riding her horse and jumping different jumps that were 2' and higher and I couldn't help but feeling really upset. I used to do that. But instead of motivating me or giving me more confidence it did the opposite. Do you guys have anything to help me?