Hello, It sounds like your girlfriend is experiencing a sciatic nerve pain or sciatica. This type of problem starts in the lower back with bulging discs which then pinch on the sciatic nerve and cause inflammation and pain as well as numbness or tingling. The best position while sleeping is usually the fetal position, being curled up on your side. Putting a pillow between the legs while laying on the side with legs bent is also helpful and relieves the pain while sleeping. Ultimately physical therapy or strengthening the core helps with relieving low back pain. Your girlfriend may need to find some guidance of a therapist to help with that. This is a very common problem and usually gets better with exercising, proper posture, avoiding carrying heavy things and taking some anti-inflammatory medication such as ibuprofen (never on empty stomach / always with food). If she is experiencing any weakness in the affected leg or problems with holding her urine or urinating in general, she needs to seek medical help immediately as to avoid any permanent damage to the sciatic nerve. Feel better and good luck! Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Kamila Seilhan, Internal Medicine Specialist