Ttc while breastfeeding

Any tips for ttc while breastfeeding? I want my kids close together I already have two age 8 months and 2 and we are trying for our 3rd and final baby with no luck. With my first two I got pregnant within the first month of trying so I’m at a loss for what to do. We have been trying since our youngest was 2/3 months old. Is it really that hard to get pregnant while breastfeeding. I use ovulation test and still no luck any tips?