Greetings, sorry about your pain.
Based on the information you provided, it is a muscle imbalance rather than a strain. Your description on what posture increases pain the most is not described by you. Your problem is loss of joint space between pelvic bone and thigh bone (femur).
Next Steps
your muscles needed to be corrected (strengthening needed) for gluteus muscles, lower abdominal muscles and stretching psoas muscles. you need to see a physio well versed in strengthening program.
Health Tips
while sleeping place a pillow between your thigh and ankle so that they do not meet while lying on sides. adapting this habits reduces pain. if you cannot find a physio or if physio treatment failed just let me know will assist you to do exact exercises to cure you from pain.