Just because you're eating well and taking multivitamins, you assume that you're getting plenty of vitamin D. According to experts, most women are not getting enough. Low levels of this vitamin is linked to heart disease, depression, osteoporosis and even cancer. It's important to have your D levels checked so your doctor can tell you how much you need and if he should recommend a supplement.
I've mentioned it before that the most natural (and the best!) way to boost your D is to let your body make it. How? Spend 10 to 15 minutes outdoors and let the sun kiss your skin, without sunscreen. I would suggest you slather on sunscreen if you have to stay longer, though.
It's hard to rely on food alone if you're looking to up your D level because there aren't many. Still, you can find it in salmon, mackerel and tuna, as well as egg yolks, fortified milk and cheese, and mushroom. Adding them to your daily daily diet will surely help.