Anyone have AS but HLA-B27 negative?

Sorry in advance for the long story. I started having lower back pain on and off about 5 years ago. After the birth of my daughter 3 years ago, it began getting worse. I contributed the pain to a rough pregnancy and figured I must have a herniated or bulging disc. I knew I couldn't have back surgery with an infant, so I've dealt with it until about 6 months ago when I began waking up like clock work every night around 2 with excruciating back stiffness. The stiffness was so bad I would have to lean against the wall until I could stretch out enough to stand. It continued for about an hour in the morning until I moved around enough to ease the stiffness. I made an appointment with an orthropedic doctor thinking I would need surgery. He said he could see arthritis in my lower disc and figured I must have had a prior injury (I haven't had an injury that I know of) and didn't give me much information and rushed me out with a prescription for dicoflenac and pain medication. The diclofenac has helped a lot. The pain is manageable but I'm concerned it could be Ankylosing spondylitis instead of osteoarthritis. (I'm only 31) I know I have been tested for the HLA-B27 gene years ago when I was suffering from unexplained fatigue and it was negative. Does anyone have AS but negative HLA-B27 gene? Thanks!