Extra long cycle in older bitch

I have a 9 yr. Old mastiff that went into season a few weeks ago. She only usually has it for about a week, it's now been longer than a month and she is bleeding more heavily now then at the start. Is this common for a dog at this age? Should I be concerned? She is still eating and drinking. She still goes outside and and plays.

Hello I suspect that there may be something behind this and would strongly reccommend seeing a vet.  You could ask to be triaged over the phone when you make an appointment, so that if the vet wants to see her immediately, then they have the chance to say so.  They might ask you about signs of tiredness, weakness or excessive drinking. Please do let us know how you get on.