If the pain has been going on for more than a few weeks a physician's in-person evaluation is in order. Initially they will probably take an x-ray or two. Don't forget to ask for the lead shield. They might order an MRI. It is not possible to suggest an etiology on an internet help column. Be prepared to provide the doctor with a timeline, stating exactly when this first started, when it develops and the intensity, as well as telling them if the pain has increased in severity.
See a dr right away! It could be a million things, but never ignore severe pain. They'll more than likely do an x-ray that won't show anything, but don't stop there. Ask lots of questions and don't leave the office until you get more tests and/or answers.
Best of wishes!