My second key to third trimester pregnancy success is to pretend like you're not pregnant. Yes, let go of those excuses you want to use so bad because honestly, it will make time go muuuuuch slower.
I am 32 weeks pregnant, and do not have any stretch marks. I'm not sure my belly button will ever look the same, but so far no stretch marks. I do have a purple mark on my belly button that is almost not noticeable, but has been there since week 16. It might turn to a stretch mark. I'm excited to see if my efforts will prove strong so I can share how to prevent stretch marks! You see, my body is raided with stretch marks from my junior high growth spurt. My calves, thighs, butt, and hips are covered in them. Literally, they are the worst leg stretch marks I have seen. When I did yoga in college, some positions stretched them out more. I seriously have NO elasticity. So my goal this pregnancy was to watch my weight gain, drink water, eat HEALTHY, and go gung-ho on the oils on my belly. I developed a belly butter routine that I will share post pregnancy :) I have had little purple stretch marks appear ever since week 16, but I have gone crazy with my moisture routine and they go away. So I can tell you right now, GET THEM WHILE THEY'RE NEW. Go crazy on them while they're fresh.