This sounds like the start of your period. This is how many girls periods start, more brown in colour. How long had it been happening for? Is it heavy? Speak to your mum, everything is fine.
Hello, my name is tiffany. I am guessing ur not having sex, so me and ur storys are a bit different. but I am having the same problem. I went to the ER for my cramps and headache and the bleeding. It could be your body is preparing to start your period. that is what she told me because brown is the color of old blood like if it was to crust on your skin. It is perfectly normal so there is nothing to worry about. If u are still worried, write ur mom a letter, and leave it somewhere she would find it or just go up and hand it to her. tell her u were embarrassed. trust me I am 18 and have been in your shoes it is totally understandable. I am here if u need to talk ok?