Im just gone 14, and very shy and quiet around friends, mostly girls i don't know!?

i mean, im a very fit person, love running, gym, and stuff .... not ugly either (not being big headed) but when it comes to being around girls i don' know, or dont ''hang with' very often i tend to be very quiet and shy... when im not! i can be quite funny and like able! so could someone please suggest as to why im awkward around girls ... and is this normal? or is there something wrong? suggestions? Thanks.