Need help!

I haven't had a period now since the end of April/beginning of May. I've done pregnancy tests and they have all come back negative. I've always had irregular periods and have seen my doctor about it before but all the tests they carried out came back negative. Just recently I've had all the symptoms I usually get (cramps, acne, back ache etc) but all I'm getting is very light brown blood as opposed to like fresh period blood? I don't know what's happening/ what this is?!