It could be caused by an imbalance between the strength of your abdominal and lower back muscles of course.
This was my situation and a few days of sit ups resolved the issue.
You can find a set of exercises that take just 5 minutes collectively if you visit our Lower Back Pain section.
Other causes range from Inflammatory Pelvic Disease to Kidney infection, though the latter would likely have in agony by now.
Try the exercises and if needs be, apply some Atrogel morning, noon and night so as to make the discomfort tolerable.
Generally, you should expect the problem to resolve itself if it is indeed muscular.
Best wishes
Earle
Do you have questions? Please feel free to ask.
Take our quick quiz to discover just how healthy your immune system is, as well as some useful information about your general health and wellbeing!