This seems to be sciatica/slipped disc.
Next Steps
Take complete bed rest for 2 days, apply ice on your lower back, take any tablet which has ibuprofen+paracetamol combination (if u r not allergic to either of them) twice a day, take a tablet which has Pregabalin (75mg) (if u r not allergic to it)...and then after 2 days, start walking around and meet a physiotherapist to start back extension exercises and proper posture