K this is weird

i just got out of the shower and when I took my underwear off I saw some light brownish stuff with the usual discharge. I keep thinking it might be the start of my period but not sure. I've never had my period before. My mum was 13 and a half when she got hers, my older sister she was 12 and 9 months. But I'm too scared to tell mum!! I'm 13 and the last in my friend group to get my period but is that what it is?? I'm so confused -_-