Add avocados, oranges and walnuts to your diet as they all help with collagen production which keeps the skin supple. As others said drink loads of water and use a good cream or oil (I use coconut oil & beeswax melted together) Put it on after your shower when your skin will absorb it best. Bio oil is expensive and is a mineral oil and similar to baby oil but about 100 times more expensive (marketing and advertising costs!). Try keep away from foods and drink that will dehydrate you (salty and sugary foods mainly) I'm 33.5 weeks and have no stretch marks and I know I'm prone to them as I have them on my hips from puberty. They don't go away so prevention is the only way!
Drink lots of water (at least 2 liters a day), keep using moisturizer. Also, make sure you are not overeating and are gaining weight gradually.
I use Aveno and Palmer's Coco Butter. 28 weeks now, no belly stretchmarks so far (Thank God),but I did get some on my breasts early in the pregnancy as they just suddenly increased in size.
There is really no 'magic pill'. Its a combination of multiple factors.
Good luck!! Hopefully, you manage to keep them down!
Any thick creamy moisturizer does the job. The skin is stretching and moisture helps with the elasticity i found
Instead of looking at them like a bad thing, think of them as a badge of honor. You earned them doing one of the hardest things a woman can do- carry a baby and give birth.
They'll never go away, but you can try bio oil to lighten them up.