Getting enough nutrients?

So, we all know as growing mommies, already existing mommies, or just being plain awesome, that it’s crucial for our bodies to get enough nutrients. We take vitamins, of course, but when you’re growing a little fetus, you need nutrients for you AND your baby. So I have been diligently tracking my food intake on My Fitness Pal (super well-known food tracking app) and constantly trying to fill my vitamin A, vitamin C, potassium, and iron bars, as well as protein. So far, I have been going strong on the first three. The key is mandarins, bananas, and string cheese or Greek yogurt. However, I can’t manage to get enough iron. Unfortunately, I don’t eat red meat, only poultry, and fish, so I know that is a factor. Chicken does have heme iron but I’m not eating enough to get a sufficient amount to fulfill the daily intake. I have tried iron supplements before but they killed my stomach and caused constipation. So I’m calling out there to you! How can a non-red meat eater get enough heme iron?