IS THIS MY FIRST PERIOD!? PLEASE HELP!?

well i was taking my nightly shower and when i shave i sit down in the shower and i was sitting down and and before i shaved i stood back up to grab some more soap and i looked at where i was sitting and there was this reddish brownish stuff and it was running down into the drain. it was at like 10:30. i'm 13. was this my first period? i haven't ever had my period before. PLEASE HELP!