Agree with nick1c, sciatica has more than one cause and there are various ways of dealing with it.
Personally physio didnt help me, however a chiropracter did. Either way, it didnt seem to want to go away on its own (even with 5 months of physio…). Best to see a professional and get it looked at properly.
Have to say a bike race doesnt sound like a particularly good idea with that ailment, but then Im just a wimp ;o)
Hope you get it sorted ok!