Can Intense Exercise Shorten My Cycle and Lengthen Flow?

For almost three months, I have adopted a pretty rigorous exericse routine of 3 days of full-body weight training and 3 days of high intensity cardio with one rest day. My last two periods have started 5-6 days earlier than usual. Also, they've been much lighter in the beginning, lasting longer with 3/4 days of spotting before AND after about 4 days of a normal, heavier flow. So basically, I've had what appears to be periods lasting about 11 days. And NOW I am starting to spot again and it's cycle day 20! It's like my periods are getting shorter and shorter the longer I've been working out. Is this huge transformation due to going from lounging around the house to working out 6 days per week? Or should I be more concerned? Will it level out? Also, I haven't been having any cramping lately and my moods are much more even....but that's a good thing, right? :^) Thanks for your help!!!