I'm not a doctor or anything, but logically, I think you need to find out the following:
1. Where is the blood coming from? Is it coming from your teeth, your sinuses, your brain?
2. Does this mysterious blood occur at any other time or under any other circumstances?
3. Do you get blood in your mouth when you go swimming or use a hot tub?
IMO, you should see an Ear Nose Throat doctor. You should probably get some sort of diagnostic scan (CT scan or MRI) to determine whether there is anything serious going on.
I hope you can figure out the problem. Please don't ignore it. It just doesn't sound normal and may indicate the presence of a more serious problem.