My last period came just over 7 weeks ago. I have been irregular but don't remember being this late. Now I'm getting very thick pasty dark brown-black discharge (sorry for that imagery). There isn't a lot of discharge though - not enough for pads, so I've been using panty liners. I haven't had sex in over a year so I'm quite certain I'm not pregnant.

Any ideas what could be wrong?

I'm getting worried and am starting to go crazy thinking perhaps I had sex with someone and don't remember - but that really isn't possible. I'm not that kind of girl. Honest.