Exercise & missed menstrual cycles?

So... Have never posted anything until now.  Have been exercising 6-7 days a week for 7-8 weeks now. I have always been some-what active, but this is a big increase in activity for me. I generally do cardio approx 30-45min each day & occasionally mix in maybe 15 min of weights (a few days a week).  I was supposed to start my period a week ago and still no sign. Took pregnancy test just to verify my thoughts, & of course: negative. So I started thinking of my recent change in my exercise pattern. Pretty certain this is the issue. I don't think my period is going to start.. I think I'm going to miss it all together which concerns me d/t osteoporosis & infertility risks with lack of estrogen. It will only be the first time this has ever occurred. So not sure it's a huge deal, unless it continues of course. Any one else have any more insight or experience with this issue? I am not underweight or anything- for the record. Thanks in advance!!;)