Implantation Bleeding?

Ok so i've been worrying for a month now that i could possibly be pregnant. I'm really scared because this morning i found brownish blood when i wen to the bathroom. I know this could be implantation bleeding and i'm wondering if i could be pregnant. I took a pregnancy test that said i was negative yet this happened. I also have extremely irregular periods like.. maybe 2 a year.. and this would be maybe the 3rd "period" of the year. And i reallllly dont know what to think or what to say... .i'm super scared and i have no way of getting another pregnancy test considering i'm out of cash and there is no way i could let my parents know. Please someone give me some advice on how i could be sure i'm not pregnant or something. I am really scared and i have no where to turn.