Is it possible for a dog to be in heat for 5 weeks or longer, She normally only lasts 3 weeks?

I'd probably have a word with the vet, 5 weeks seems a long time. My Girls are usually in season for 3 weeks. I thought this was the norm. I may be wrong though as breeds may alter,but 5 weeks seems a bit too long.

I have had a bitch be in seaso for 4 weeks, and also had them appear to come in season, stop and start again in a wek or so, so if I hadn't been obserbant may have assumed a longer season.

I would still get her checked for any infection at the vets.  I usually say that it is best to keep bitches away from male dogs for up to 4 weeks, as conception on day 23 or so is not that unusual.