Does implantation vary when you have an irregular cycle?

I'm very irregular normally my cycle last for 30 plus days but this month it ended really early and most of the time I was spotting and then for about a week I had brown spotting! I started on the 18 of last Month and ended on the 3 or this month! Has this ever happened to anyone else? And I also just started taking prenatal vitamins could that be changing my cycle?