bras?????

So I'm late 13's and am already mid way through puberty. I usually wear spots bras because I'm pretty athletic and my sports bras aren't that restricting and are comfortable, but lately I've noticed my boobs have been growing more and I feel like most of my sports bras are making my boobs hurt from too much restriction. I want to go shopping with my mom but every time I want to bring up the subject I chicken out or am interrupted by my brother or dad. I know it's time to get a real bra but I don't know how to ask without my mom feeling sad that I'm growing up, or make my dad feel weird about the fact that I have boobs.