Boobs

I'm 23 & I have been ordering the same size bra since I was 17. Before that I was flat chested i basically didn't grow curves till I was 17. Well at 23 I couldn't fit in my bras just the pull over sports ones. I am now a 34 C & for years I was a 34B. Is that normal that they grew at this age. I even have strech mark on them now. & no I'm not pregnant it's been 6 months & took a test