No period 70 days

Hey guys!

First off, not pregnant unless I'm Mary 2.0.

I haven't had my period since May. It's September now.

I have no real symptoms, no cramping or pain or anything.

Maybe a bit tmi, but all I have is clear discharge, like I'm in the fertile window.

I'd like to go to a gyno, but the one near me only takes people 18 or older. I'm not that age yet, and don't really want to wait a few more months if there's something I can do now.

This has happened before, but they just told me it is cause I'm young and put me on birth control. They wouldn't listen until I missed 72 days, either. Once they told me it's cause I gained weight, and if I lose some it should even back out. It hasn't.

Once I come off birth control, my times slowly increase from my usual 30 days between periods to 45, 50, 60, and now 70. This happens every time, and I've been on birth control for this issue 3 times now.

When should I start to worry? Could this be a sign something is majorly wrong? What can I say to make my doctor listen to me this time and not brush me off?

Thanks for any advice!!