Thanks for your query.
You should go to an orthopedic surgeon and get yourself clinically evaluated.
AP and lateral view of X Ray needs to be done of your lower back.
It might be simple muscle pain
.Or there may be fracture of vertebra or disc prolapse
. There may be injury to spine as well for which MRI would be needed... Are you having problem in moving your legs ?
For pain you can take Aceclofenac Paracetamol
combination tablet and local application of diclofenac
gel.But it is better not to self medicate but to get advice from your doctor.
Hope this helps.