Is it unusual for a 13 year old girl to have hardly any , but has had her period?

I am 13 years old and I have had my period like 10 times. I have hardly any s, and I feel kindof jealous when some of my friends come over for sleepovers and when we change into our pj's, they unchange in front of me and also take off their bra. Every single one of my friends always take off these like big padded bras. Then once the bra is off, I see their and they are like so big compared to mine. I only wear a sports bra. All my other friends have their periods and wear padded bras. I dont know if there is anything wrong with me or not. Should I just try to convience my mom that I want padded bras so my s wont sag? I really dont know if it has anything to do with my period. Help me please!!!!!!!!!!!!!!!!!!!!!!!!!