Stretch marks?!

How are you preventing strech marks? Did you notice any strech marks during pregnancy or it only appears after birth? I know my body won't be the same but I'm kinda freaking out with stretch marks on my boobs! I always had big boobs and now it is just getting insane lol I'm 25 weeks and I'm using lotion and oil every time after shower, and sometimes during the day if my skin gets itchy...