Brown blood in panties after fingering? Period was 10 days ago?

I've been with my boyfriend for just under two years, messing around for about 8 months? After today's messing about, I went to the toilet and saw that my panties were covered in this brown discharge or blood? I don't have any idea what this is? Sometimes I get it the day after, but not usually this much. I'm not on birth control, and there is no way I could be pregnant, we're very safe! Can someone please help me out? I'm worried!

Thanks x