Periods & Bras. (GIRLS)?

Heeyy. I'm 13 and going into the 8th grade, and 4-5 months ago I saw a brown spot in my undies. I know this is just a dried blood stain, but I'm really wondering if this is a sign that I'll be getting my period soon or if it IS my period. If it's just a sign, then how long will it take for my period to come? It's been a while, but I guess it could sometimes take a long time, right? Also, my breasts are smallish. I wear undershirts and those little training bras and those seem to do the job. Although my mom said it may be time for me to get a real bra, but the last time we went bra shopping, no bras fit me, and that was like 2-3 months ago. Anyways, I dont think it matters what breast development stage im in in order to get my period, right? Please answer my questions informatively(if thats a word..)