Why Am I Having Light Dark Colored Periods?

hi i am 31 years old no children but sexually active...i have irrigular menstration problem since i was 24...my period is once every 3 months and it will last for 5-6 days. I dont feel anything in my body im strong and active in my daily life activities. but this time my period is very light , dark color and will last only for 2 days. is there any herbal medicine or vitamins i can take to make my period last longer and make my menstration period regular? i really appriciate any answer.. thank you