So you wax your vehicle every three months? Well, that puts you way ahead of most people. Keep up the good work.
As to the question, "How often should I wax my car?" I like this rule of thumb: apply a fresh coat of wax whenever a characteristic that you value--gloss, slickness, beading, wetness--degrades to an unacceptable level. Besides, it can never hurt to apply a fresh coat of wax, and the car always looks better.