I have has a massive headache for three days my vision is blurry and im very dizzy why is this?

Need to find out. Asap! get someone to take you to er.
Many possibilities. Several things may cause symptoms like that (migraine, sinus infection, tension headache, etc.) but some serious conditions should be ruled out, like tumor or bleeding, glaucoma and several others. Please get checked as soon as possible. An emergency department would be a good start if you do not have a doctor who can see you immediately.