Hello, and thankyou for approaching DoctorSpring with your query.
From the symptoms you have described of pain on movement, it does seem to be a muscle pull. It probably developed from sitting in a slightly wrong posture for a long period of time or a sudden twist that caused the pull. It is nothing to worry.
I advise you to take an analgesic + muscle relaxant drug. If not, you can take the OTC drug Ibuprofen twice daily for 3 days after a meal.
Do warm water compresses, or take a hot/warm water bath and let the water flow on your lower back for atleast 5 minutes as this will help your muscle relax.
However, if you feel that your pain is spasmodic , urine has decreased, any nausea or vomiting associated with it, you will have to go to the medical center and get yourself examined.
I hope this has helped. Wishing you a speedy recovery.