Chronic lower back pain

I have had lower back pain for the last 3 years. It first started as pain in the left SI joint. Was given anti-inflammatories and diazapam but they didn't help. I then started getting more stiffness especially in the morning and some pain in the back of the right leg - mostly the top part but occasionally it went down to the ankle. I was then x-rayed and had blood tests which showed nothing. Had Physio and core stability exercises which didn't help. Had an MRI which showed nothing. I kept returning to the doctors but they just said it would get better or I would just have to get used to the pain. They told me to stop looking for a reason why my back hurt and suggested I took anti-depressants. I have spent over £1000 on chiropractors, osteopaths, physio, hypnotherapy, counsellors, acupuncture, nutrional supplements, a new bed, new chair, changed my job, do regular exercise, but to no avail. My back is worse now than it was when it first started. I have pain all the time but sometimes it is just in one joint, sometimes just the leg, and others in both joints, leg and back at same time. A recent osteopath suggested I see my GP to be referred to podiatrist as my ankles turn in and i have flat feet but the doctor said i was clutching at straws and recommended the alexander technique instead - he wouldn't refer me. I was also told I might have a stuck SI joint on the left and a hypermobile one on the left. I'm at my wits end and really don't know who to trust, who to turn to, and what to do to resolve the problem. I just want it fixed. I'm only 29 - i've not had any accidents to cause a back problem either. I'd appreciate any advice you can give.