What Causes Migraines, Head Pressure, Dizziness, Lightheadedness, Sickness With Sharp Pains?

for the past month or so i've been having dizzy spells and getting light head frequently. then out of nowhere i will just start feeling sick. i will start gagging at times but have yet to throw up. lately I've started to have sharp pains accompanied with the sick feeling. i get migraines and then sometime i feel like this pressure is in my head like someone is pushing on it. any idea on what it could be?