How To Identify Signs Of Menarche?

I'm 12 and haven't had my first period yet, starting today I have had a brownish with a little red discharge and when I wipe my area there's some red on the toilet paper. I haven't had any cramps so I'm not sure if this is my period. I use a thin pantiliner to keep from staining my clothes and tomorrow I am going to the beach with my friend and I don't want to stain my bathing suit, so what should I do and is this my period?