What Is The Cause And Treatment For Back Pain?

Hello, I am an 18 year old female. I have had lower back pain for years, I am not quite sure when it began. I am an equestrian and started to first notice my low back pain when riding, it s gotten worse over the years now. I have done physical therapy two separate times, no results. I have had an MRI of my lower back and hips (I started getting hip pain about a year ago and have found exercises to help with the outside hip pain but hip pain in my groin area will not alleviate), an x-ray of my hips, and a couple years earlier I also had x-rays of my upper back. Everything has come back with no problems. My pain is becoming more constant. Bending over and riding is when it is at its worst. Simple tasks such as tying my shoes, feeding my cats, cleaning their litter box, hand washing dishes, and vacuuming cause me pain. I also noticed my tailbone is sensitive, sitting on a hard surface hurts. I am not very active at the moment, however, I used to be very active. I was in very good shape, riding all the time, working out, but the back pain was always there. After a little while of riding my back seems to quit on me, I get stuck in a very arched position that I cannot get out of unless I bend completely forward (which is not ideal for riding) and my breathing changes a bit I have noticed. I am fully aware of what it is like to have labored breath from exertion, this breathing is different. It feels tight, I get a little rasp, and it just altogether feels a bit harder to breathe. I do not think it is asthma. I have also noticed that I have a more excessive curve to my spine than normal, not scoliosis. It is not a fixed lordosis, however that is where all of my pain seems to stem from is in that curved area. The only thing that alleviates the pain there is to round out my back. I have seen an orthopedic doctor and was very discouraged by him because he seemed to dismiss me since there was nothing wrong on my MRI or X-Rays. He says to keep doing my exercises, but they are just not working and are making the pain much, much worse. I have very hard times sleeping and getting into a position that does not hurt. I am at a loss here. I am not sure what my next move should be, who to see.