My cycles are getting longer

I've noticed this entire summer my cycles have been between 35-40 days long and at it's been a source of stress all summer long. When I don't get my period I think I'm pregnant and when I get my period after a long time I'm afraid their may be something wrong with my menstrual cycles. I've read that long cycles can be an indicator of anovulation. Has anyone else experiences the same things? Or does anyone else know what else couldn't possibly be going on. I'm going to see my doctor in 2 weeks about it.