Thanks for writing your query.
It seems that you had a muscle pull while bending.
Take proper rest. Hot fomentation and application of pain relieving gel will give you some relief in pain.
You can take pain killer like Ibuprofen
one tablet twice a day after meals with antacid Omeprazole
20 mg along with muscle relaxant
like chloraxazone. This will relax the sprained muscles.
If the pain persists, get yourself examinned by your doctor.
I hope this is helpful to you.