What is the first thing to do if I have pain radiating from the butt to the knee down the leg. I have no swellings. What should I do next to get relief.?

Sciatic pain. Conservative measures are always good to try first. Resting, ibuprofen, heat/ice, very gentle stretching of the hamstrings and lower back. Avoid lots of bending over, lifting things... But don't be in bed all day. If you have fevers, are wetting or stooling yourself, or any significant weakness in your leg, you need to see a doctor asap.