atlas slips out of place causing severe neck pain

I have been in physical therapy since October for neck pain. I have been told the pain is caused by my atlas slipping  out of place. I have not been able to have an xray because I am 11.5 weeks pregnant. When I go in for physical therapy, my physical therapist manually puts my atlas back into place after I do my stretches and traction. My atlas slips back out of place within 3 hours after I'm done with physical therapy. I have noticed no significant improvement after 3 months of physical therapy. I continue to go because it is a way for me to manage the pain without medication (most of which I cannot take because I am pregnant). The neck pain is severe at times causing terrible headaches and at times nausea (although the nausea might also be caused by my pregnancy). Who should I go see to get relief from this constant pain? My regular physician has told me there is not much we can do because I am pregnant but I cannot imagine spending the next 6 months in this kind of pain.