What is causing my high blood pressure? (I usually have very low blood pressure)?

For a few days i've had a terrible head ache and I think it's the blood pressure. The thing is, my blood pressure is usually like 99/56 Low normal but that is my normal.
Recently i felt restless and have a bad head ache... i checked it at the pharmacy and it read 117/75, that's really high for me. I have a big project due in a week, and i've b een stressed about that. i'm also riding my bike more, What could be the cause, how do i get rid of the headache?