Numbness in your left hand and joint pain after a car accident may suggest nerve compression, nerve root irritation, joint injury, or a fracture, so it should be promptly evaluated by a doctor. You should avoid taking medicines or injections on your own and instead undergo a proper clinical examination with imaging if required. You may use over-the-counter pain relievers such as paracetamol, diclofenac, or ibuprofen to help with joint pain, provided you have no stomach, kidney, or bleeding problems. Avoid heavy lifting or sudden neck movements and keep the arm in a neutral position until you are examined.

Given your long-standing back pain, now with new sciatica (sharp, radiating leg pain due to compression of the sciatic nerve), you should see a doctor promptly for a proper examination and possible imaging. Try to avoid prolonged sitting or standing and maintain gentle movement rather than complete bed rest. Simple pain relievers such as paracetamol or ibuprofen may help if you have no contraindications. Seek medical care immediately if you develop leg weakness, numbness in the groin area, or any loss of bladder or bowel control.