Is It a Somatization Disorder? (Osteopathy Specialist)

Medical Case Details:

A 20 years old female presented to my clinic with the complaint of lower backache from last week, which was radiating both upward and downward to both lower limbs from the posterior aspect. There was no aggravating or relieving factor and no constitutional symptoms. After examination, I found that she had a list on the left side, and her straight leg raise test was positive without any neurological deficit and hamstring spasm. I started treating her for acute PIVD by giving bed rest, NSAIDs (nonsteroidal anti-inflammatory drugs), physical therapy, and neuro vitamins. Her pain subsided in one week, and I started her on back strengthening exercises. As per her mother's opinion, she was 100 percent pain-free. After a month, I again saw her in my clinic. She said that she stopped doing exercise, and the pain also started again. This time I asked her to get an x-ray and MRI (magnetic resonance imaging) of the LS (lumbosacral) spine done. I was expecting some disc prolapse. Surprisingly, I could not see any disc prolapse, any collection, or any deformity. I asked if she had any other joint pain, but she had the only backache. This time she said that the severity of pain increased in the morning. I asked her to get work up for inflammatory arthritis. But all those tests were negative. Any suggestion on what I am left with?