Compare on breastfeeding duration

Mil has been comparing me with sil on how long I breastfeed the baby. I don't produce bm as much as my sil, and I struggled to breastfeed until my baby was 6 months old. On the other hand, sil is oversupply, and she can breastfeed her 2 kids with her bm with extra supply. Mil says cause I don't take care of myself well, which caused me to be low supply on my bm. Honestly, I did all I could, but I'm at wits end when it comes to bm supply. I'm currently pregnant with no.2, and I'm scared about breastfeeding, to be honest.