Stretch Marks but not growing??

I have fairly big boobs to begin with (32DDD) but i grew into them slowly throughout high school-never had stretch marks on them. Im now 23 weeks pregnant and notice new stretch marks forming on the bottom of my boobs but i truly don't feel like they've gotten any bigger? Can you get stretch marks without growing any? Am i just delusional about my boobs not growing? I still wear my same bra and it's not uncomfortable or anything.