What Causes Lightheadedness And Dizziness?

for the past few days i've been feeling really lightheaded and dizzy. Yesterday morning i woke up and had to sit on the floor, i was then sick after having a drink. I was also sick again this morning and i am still feeling dizzy. My period came the day before yesterday its slightly early and lighter than usual. Im so thirsty constantly and tired! whats wrong with me?