Weird Period

Hi,

i'm a new member! My problem is this: normally i'm very regular with my periods, they come every 35 days and they are heavy the first two days and last an entire week. But in april, my period was two weeks late and only lasted 4 days, so I took two pregnancy tests which were both negative.
This months period was supposed to show up on the friday that just past, however it showed signs a week earlier. I was expecting a heavy flow as usual but what I got were clumpy clots of red/brown that i'm guessing is old blood that only came out when I was on the toilet. I haven't had to use anything like a tampon or pad. Technically if that was my period it should've ended by now but it hasn't.
I'm not on bcps or any kind of medications, haven't had sex since the end of march and haven't been sick lately.
Anyone have this problem before?
Leminh