I have irregular cycles i have one every 4 or 5 months no pms symptoms but it last about 3 weeks heavy heavy heavy. what could that be ?

Irregular periods: It probably is suggestive that you are not ovulating every month and that your endometrium eventually becomes so thick that the uterus must expel it giving a hard and heavy period. It probably would be a good idea to be evaluated by a gynecologist, have an ultrasound and perhaps be placed on oral contraceptives to regulate your cycle.