Hey man, I never had sciatica as bad as you but I got it in my left buttock once I stopped being active and playing computer games.
Avoid things like tight belts, low hip trousers & things in your back pocket when you sit down. Also avoid sitting down for long periods of time. Daily hot as you can bare showers will help too and also try self massage too.
The thing that will ultimately help you is something like Yoga or Pilates. The stretches in these 2 arts will treat your whole body which is whats always needed... (one part off balance different problems etc)
There are other quick fixes though:
Lie on your back and allow your lower back to touch the floor. Lift your knees up to your chest and hold them with your hands. Lie down that way, the spine stretch gets more intense if you flatten your neck too. Lie down like this for a minute or two but don`t do it if it feels painful.
Best one for sciatica is to sit down on a suitable chair and put one foot over the other knee. The side of the raised foot will get a nice stretch. The stretch is intensified by straightening your back and/or leaning forward. Lean slightly towards one side (opposite side to the one being stretched) and bring your forehead down to your knee.
Don`t do any of these on any sort of pain meds, if they feel good keep doing them as required. Not too much but listen to your body.
Hope this helps man