How long does cortisone effect dogs for when using it for an allergic reaction to a bee sting. Are long urinat?

I took my 11 mo old dog to the vet 5 days ago because he had an allergic reaction to a bee sting, he accessive urinating, which i was told would happen, but he is peeing for 2 min constant for every time he goes to use the bathroom. It is clear. Should I call my vet tomorrow? Or is the drug just effecting him this way?I was reading that the shots last 8-12 weeks, so should I be expecting this amount of urination for that amount of time?