consistent late periods ... but .

So I've consistently had late periods . Many times I would swear up and down I'm pregnant , take a test and it would be negative . I then thought , hmm okay something might be wrong with my lady health . Let me get checked out. So I went to the doctors , had an ultrasound and also some bloodwork to see if my hormones were off or if I have pcos. Everything came back perfectly fine .  And here I am again late , have nearly missed my entire period ... I'm on day 37 of my cycle and STILL no period. This is the latest I've been. It's frustrating because there is noexplanation  behind it . I'm not ttc at the moment but in a few years I want to have a baby .. and I'm worried that it's going to be difficult to conceive because of my irregular cycle . Does anyone else have this with no explanation as to why ?