Fever after MMR - how long will it last?

[sausagedoesnotroll]

DS had the MMR just over a week ago. Unfortunately he came down with a snotty bug the same day, so I'm not sure which symptoms relate to what.

He's been a bit grizzly all week but nothing serious, but yesterday he got a fever. Since the nurse told me he might have a temperature as a result of the MMR about a week after having it, I'm guessing that's what it is. We gave him Calpol but it's back up again as soon as that wears off. General advice seems to be "contact your GP if the fever persists". Does anyone know how long it's usual for a fever as a result of MMR reaction to last? How long should I wait before taking him to the Dr?

Thanks

[CantSupinate]

3 days or more of fever b4 contacting gp, I reckon.