dark brown to kinda black discharge,what is wrong wit me?

i did not track my cycle length before,until April 2007.And since then its been a 30-42 days cycle ocassionally its 53-56 days.And today is CD-44.SInce last few days i've been having dark brownish to black discharge,sometime its yellowish to light pink.I did a HPT on CD 31 and it turned out neg.I never experienced this in past AF.My body feels heavy,n legs feel numb when i take a rest.besides that no any cramping like past AF.I can't seem to figure out what is going on.My app. is in July.I'm scared,i can't take HPT cos' i'm not confident enough.i think i've BD on possible O days(through certain signs).Though i'm not so sure if i ovulated. I need some suggestion here.what are the chances that i MIGHT be preggo? I just need a little guide as i'm totally lost.