pain in the bum

recently my right glutemus muscle has been hurting. it goes when i run and comes back the day after. it gets worse if i try to rest it for a few days or more. I have the sheffield half in april and trying to smash my time for this race so not training, not an option. I have tried the sink stretch and squats to strengthen it.

Now i have got the symptoms of a cold coming on that wont come out or go away. so this might be one reason.

any advice?