First bra situation, need help ASAP?

Ouch. I am 13 too, and I had to wear undershirts FOREVER. You need to tell your mom that you're growing now and you really need one. An option COULD be that your nurse or school counselor could help too. Next time your at the doctors, ask if you need a bra, mention you feel uncomfortable without one and surely the drs will back you up. Hope I helped. Good luck.