Can't get pregnant while breastfeeding?

Hello everyone 😀

The situation is me and my husband have been trying to get a sibling for my daughter since like 5 months ago, I keep track on my ovulation and we've been getting busy in bed as soon as I'm at my most fertile window, but I still havent been able to get pregnant. Could it be because I'm breastfeeding my 11 month old daughter? Help. What can I do to get pregnant?!