What’s this hard lump under my nipple?

i’m a guy by the way. i just noticed it this morning but i’m not entirely sure if it was there before or after my brother and i were messing around. he accidentally punched me in the spot. it didn’t hurt much but when i was in the shower lathering up, there’s a hard lump directly under there. it doesn’t hurt or... show more i’m a guy by the way. i just noticed it this morning but i’m not entirely sure if it was there before or after my brother and i were messing around. he accidentally punched me in the spot. it didn’t hurt much but when i was in the shower lathering up, there’s a hard lump directly under there. it doesn’t hurt or anything but i’m a tad worried. what should i do?
Update: i forgot to mention im 16 and a half
Update 2: i already had my growth spurt shortly after turning 11, it was fast and i haven't grown much since. idk if it matters
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