Most likely due to muscle spasm.

This treatment is being suggested on bases of the information provided. However I would like to examine & investigate you  in detail. Control  Hypertension, Diabetes or any other metabolic disorder, if there is  any. Any way it may be tried, --. Dolokind Plus (Mankind) [Aceclofenac100 mg +Paracetamol 350 mg] 1 tab. OD & SOS. X 5 days. --. Caldikind plus  (Mankind) 1 tab OD x 10 days. (You may need help of your local doctor to get these medicines.) --. Fomentation with warm water. Let the part not be exposed to cold. --. Sleep on a hard bed with soft bedding. --. Use no pillow under the head. --. Avoid painful acts & activities. -- .Do mild exercises for  back and hips and knees and . --.(Take help of a  physiotherapist). --Do not ignore, let it not become beginning of a major problem. --Do ask for a detailed treatment plan. Kindly make sure, there is no allergy to any of these medicines. --For emergency treatment visit nearest hospital. --Wish you a quick recovery & good health. --I hope, I have solved your problem to your satisfaction.  Dr N C Gupta MS (ortho)

Yes you can add physiotherapy like IFT too

Take tab Combiflam mor and evening for 5 day Otherwise come for consultation

Hi.    with your complaints it can be lumbosacral strain need to be evaluated...with examination to conclude and treat further...now you can take some muscle relaxants like tab hifenac MR twice a day..