It sounds like classic sciatica.Take paracetamol and ibuprofen, keep moving gently, keep your back as supple as possible with whatever exercise suits you, yoga, pilates, tai chi, chiropractic or osteopathy treatment may help, if they're difficult to access, ask your doctor for a physiotherapy referral. Rest when you need to, but DON'T take to your bed and stay there - bedrest will cause more problems than it cures. Seek medical advice if you experience altered sensation down your leg or foot, or have altered saddle sensation (which would lead to difficulties with passing urine and/or defaecating). Most back pain resolves over a few weeks/months without any treatment other than the things I've suggested, and is miserable to live with! Best wishes.