Ttc while breastfeeding

Can someone help me understand why I keep getting my period at 4 dpo? 😞

This is our second month trying and both months I’ve ovulation tested every day, I’ve ovulated on day 23 the first month and 21 the second and both times 4 days post ovulation I’ve gotten my period.

My nearly 15 month old son is feeding twice a day (11am and 6pm) and short feeds for about 5-10 minuets.

Do I need to completely stop feeding? I really wanted to feed until 2 😞