Extension Exercises x 15 times x twice daily - lying on tummy, take left arm up for 3 seconds, then bring it down, right arm up for 3 seconds, bring down. Bring right leg up, hold for 3 seconds, bring it down. Then right leg up and hold for 3 seconds and bring it down. Repeat twice a day- 10 times. Bhujang Asana -- Lie flat on your stomach, keeping the palms out, bend the neck backward, take a deep breath and while holding it for 6 seconds, raise the chest up. Release breath and relax your body. Repeat the exercise 15 times twice daily. Core Strengthening Exercises- Straight Leg Raised With Toes Turned Outward, repeat 10 times, twice a day.

Could be due to muscular or ligament strain

You may have strained your back due to incorrect posture or injured it while lifting something. If the pain is limited to the back then rest, Pain killers and continuing with regular activity will help you. If you start getting any pain in buttocks or pain down legs then see a Spinal Surgeon for assessment and investigation.

See a Spine Surgeon, u never know how bad your back is so don't take it lightly or experiment with vague excercises or analgesics

You might be having mild disc bulge at l5 level, so kindly visit a physiotherapist and have proper physiotherapy for 1 week and learn ergonomics.

May be you having disc bulge but other investigation required.

Start with back strengthing exercises.  Sending you the link of the same https://play.google.com/store/apps/details?id=com.backpainrelieving.backpain Or you can search for " back pain relieving exercises by kavin khatri " on google playstore