Ok these stretch marks are bothering me?

im 29 weeks pregnant and im not that big at all,,i have people ask me how far along are you and i tell them 7 months and they have an amazed look on there face and say your so little..like theres girls that are 5 months pregnant there that are bigger then i am..and im not a skinny girl but im not a big girl..im curvy a good shape..but like since im not that big why am i getting these stretch marks and ive been using lotion but its not doing anything..ive tried regular lotion,,pregnancy lotion..and ive used that palmer coco er lotion but nothing working