stretch marks are notoriously hard to remove, even if you use the most expensive creams out there. The ones that form during pregnancy are caused by your skin expanding to adjust to the baby growth, and then retracting after the delivery.
For your future pregnancies you can try and prevent more from forming by using some cream against stretch marks while your skin is stretching, but that is about it that you can do.
There are some expensive laser treatments that claim to completely remove stretch marks - I haven't tried them, but they do seem to be far more successful than just applying anti-stretch marks cream alone,
Wish you all the best,