IF may tank your breastmilk supply depending on how your body reacts to stress. It’s one of the reasons I didn’t start IF until 3 years post partum.
Cutting calories -> supply tanked,Longer periods of non-eating -> supply tanked,Work stress, sleepless nights due to baby, exhaustion -> supply tanked
Some things are controllable while others are not. Having too many stressors could lower your milk supply too low.
Definitely talk to your doctor about this first because the last thing you want to do is start calorie restriction and have your baby not get the nutrients they need. There’s a reason IF is generally not recommended for pregnant and nursing women.