Do i have a cavity ? what about the needle ? scared !?

okay, well i'm 13 and afraid i have a cavity. can you help me determine if i have one ? thanks . okay well sometime when i eat something really chewy and sticky certain parts of 2 teeth in particular like not hurt bad, but i don't know how to explain it, it's kind of just like a little weird feeling that kind of hurts a little, not bad at all. but this never happens when i eat something normal. i have braces. ( if that helps at all ) i heard about people saying holes in teeth that get brown ? well i look at my teeth and on one there a tiny tiny tiny brown dot on it ? cavity or no ?it's really small. i'm not sure if it's on the tooth that hurts or not, and i had a Novocaine needle before and it hurt soooooo sooooo bad ! and i absolutely am a big baby when it comes to needles. and i do not want to have a cavity. do you think i do ? thanks so much !