Hey mummy, I was an exclusively pumping mummy for 10 months before I stopped breastfeeding - I did end up with stretch marks on my breasts, but they weren't as bad as the ones on my stomach. It took me 11 months postpartum to finally be okay with looking at myself in the mirror :/ What I'll say is to learn to love yourself, pregnancy and having a baby does so much to our body - we shouldn't try to be mean to ourselves either! It'll take a while, but it does get better with time because they'll fade ... And I feel like they are our "battle scars" :) You're doing a really good job already mummy, don't be too hard on yourself!
Try putting on stretch marks cream or bio-oil before you go to bed every night. Might work to reduce stretch marks over time.