I'm so confused!

Rosy
My cycle has been totally crazy lately. 
May cycle: 4th-8th
June:5th-8th and again 6/29-72
July: 6/29-7/2 and 24th-28th 
I've had nothing this month BUT on 8/19 I had dark brown spotting, but only when I wiped. 
I've taken HPTs and they're all negative. I'm so lost and confused. 
I have no idea what to think.