At which stage will we have stretch marks? Does the stretch mark cream helps?

Usually late second or third, however, you may or may not have stretch marks as it’s mostly due to genetics. If your mum has them, you will probably have them too. It definitely helps rather than not applying anything at all. My mum had stretch marks and I have been diligently applying since week 5, I thought I could escape stretch marks but it appeared at week 38 🥲.