I am 45 and I had a ligher than normal period. I am having dizziness, nausea, and sleepy when the dizziness comes. Could I be pregnant or what could it be?

It could be a lot of things other than pregnancy. At 45 you've had lighter or heavier periods before. If you are concerned you should visit a doctor to be examined. It might be a virus or it might be a number of things.