When does ovulation continue after child birth if you breastfeed?

I had my baby 3 weeks ago. I pump 4 times a day. My baby hasn't really liked direct feeding. I give him formula when I run out of breast milk every day. I don't produce a lot of milk. I was told woman who breastfeed take longer to start ovulating. How long does it usually take? We haven't started having intercourse yet but we do get intimate & I just want to make sure we are okay when we start.