Period different: should I be concerned?

Hello Sisterhood,
This is a topic is usually discuss with a Doctor but since they're closed until after new year I'm not too sure what to do.. I think if I go to emergency they'll just laugh at me or get mad for me wasting their time but I'm concerned something is wrong.
Anyway here goes. I have gotten my period 2 weeks early and it's very different to usual! Usually I can pick up on my period symptoms for up to a week beforehand, and I only bleed heavy for the middle 3/4 days. This time it's at least 3 times as heavy, a lot more painful, very early and the blood is quite dark. I'm usually very regular and very in tune with my body, I'm not sure if its relevant of not but I've been using the same birth control for about 12 months straight now, and I do have 2 kids, the youngest is 15 months.
Does anyone know what could be wrong if anything at all?