
hi, about 3 weeks is average but some can vary, my only experience of prolonged bleeding im afraid is my girl who has failed to concieve 2 seasons running, she has had thyroid tests, blood tests and next we are going to check for cysts on the ovaries too. her bleeding continued until about day 41!
how old is the bitch and what is her usual pattern (if she has had a few seasons) if only a 3 weeks then dont panic yet she could be completely normal, obviously just keep a close eye out for any changes that seem unusual.
regarding the first season some girls have long seasons the first time round, one of my girls bled for 5 weeks on her first season and she is a normal healthy adult and pregnant now. :)