I First Felt Some Slight Lower Left Back/at Top Of

I first felt some slight lower left back/at top of hip pain after mountain biking last Saturday. Got worse with shooting pain on Sunday while doing normal household chores. Monday got better with complete rest and today's rest did not reieve completely but rather today it got much worse. Aggravated by sitting u and hard to sleep on bacjk or especially left side. Likely muscle strain but wondered if kidney problem. Thoughts?