I just recently started working out again after 3 years of a long vacation from the gym. I have noticed that after my workouts, I get these horrible migraine headaches that last well into the next day. I find myself living on Advil. What do you think this may be?
I do aeorobics for 1 hour and weight training for 45 minutes.

Headaches after exercising will be caused by vasodilation and then constriction of the blood vessels. When you do aerobic exercise - this is exercise in the presence of oxygen, you vasodilate, that is your blood vessels open up to allow more oxygen to get to your muscles. Once you cool down, they all vasoconstrict back again and that is the time when you can get a headache.

I would suggest that if you have only just started exercising again recently, that you do not do aerobic exercise for an hour. Cut this down to 30 mins and see if it helps and also reduce the weights that you do, until you get back to full fitness. You need to build up gradually rather than doing things all in one go.