Am i just being hormonal?

Sa
My SO looks to his sister for any advice on pregnancy. She has a 7 month old. I am currently 17 weeks 2 days pregnant with my second child, his first. My doctor has instructed me on foods I can and cannot eat. My SO was all for keeping those foods out of the house until she told him that I could eat those foods as long as they were cooked right. As for eating healthy food, that's all my SO would buy because he wanted me to eat better. Until his sister told him that she ate whatever she wanted when she was pregnant. Now it's not such a big deal to him anymore. But when it comes to having a fountain coke once in a while (even though my doctor said it was fine) is apparently one of the worst things I can do, because his sister said it was bad for the baby. I get that he's concerned because this is his first child, but it's not my first. At what point do I put my foot down? Or am I just being hormonal?