It sounds like you might have sciatica pain. Is the pain radiating towards your little finger of left side? There are many issues to consider here including your weight posture
calcium levels BMD and lifestyle. Try and visit a orthopaedic or PMR consultant for confirming diagnosis. You may be advised to initially rest and take medication for few days followed by physical therapy (physiotherapy).
Next Steps
Try some over the counter painkiller. Do NOT bend your back while picking something from floor. Avoid heavy weight lifting. Wear a orthopaedic belt if it helps. More details would be needed go give specific treatment. All the best. Hope you get well soon.