Brown stuff in my underwear and it doesn't' smell bad

Hi my name is Ashley and I have been having some problems I'm 13 and I have been having brown stuff in my underwear and it's been coming from my vagina and it doesn't look like there is blood in it I haven't started my period and I have been having this for a couple days now and it's making my stomach hurt but the upper part of my stomach and I'm not on birth control and I haven't had sex and at first I thought it was poop but it's not and I think it's brown discharge but I'm not sure and I have tried wearing a heating pad for my stomach and it doesn't help I have tried wearing different underwear it haven't done anything and it leaks through my pants and my underwear if I don't wear a pad or a tampon and it doesn't smell bad so I really need help my step mom says it's my period but it's not red and it drys up and it doesn't look red