When did you start getting stretch marks?

I don’t know why but I have terrible self body image... I have wanted nothing more than to be a mother and have always been in descent shape, I work out 3 times a week and did 5 times a week before being pregnant. I was 140 lbs before baby (curvy figure) and have gained 25 lbs. I’m currently 28 weeks pregnant. I have old stretch marks on my hips that you literally can’t see but I’m just wondering when everyone started getting them on there belly region? Or if you got them on your belly at all even if you had them on your hips already like me. I am terrified of not being sexy for my husband after baby, even though he is the sweetest guy & always reassures me.