It is not uncommon for a dog to bleed for up to three weeks while in heat. The length of the bleeding period can vary depending on the individual dog. Here is some information gathered from the search results:

1. The heat cycle of a dog typically lasts about five to seven months, and a typical heat period with bleeding can last two to four weeks [1].
2. During the heat cycle, there are four phases, and bleeding or bloody discharge occurs in two of these phases [1].
3. Bitches usually bleed the most in the first week of their heat cycle, but it is not uncommon for bleeding to continue into the third week [2].
4. Some dogs may bleed more in the third week of their heat cycle [2].
5. The amount of bleeding can vary between dogs, with larger dogs often bleeding more than smaller dogs [3].
6. It is important to note that all dogs are different, and their heat cycles can vary. Some dogs may have shorter or longer bleeding periods [2].

Learn more:

1. Dog Heat Cycle: Length, Frequency, and Stages
2. 17 days and still bleeding? | UK Pet Forums Forum
3. Dog in Heat (Canine Estrus): Symptoms and Spaying