Whats going on??

So my period is really late. I haven't even had it at all during the month of August! And still nothing!!

The thing is, I've experienced cramps, and that weird brown/old blood I always get before my period. But that stuff went away and I still don't have my period, which I usually always have after that stuff.

I took three pregnancy tests and all came back negative. I'm relieved, but I still have no period.

Please help? What's going on??

(By the way, I have no insurance of any kind, so going to a doctor isn't an option. Plus I'm under 18 so my family CANT know I went to some doctor about this)