So sad😢Have to stop breastfeeding in one week

Mi
I love breastfeeding, so do my baby. He will be five month old in a week, EBF since birth. 
I just diagnosed with a very rare autoimmune disease, which my doctor believes triggered by pregnancy and childbirth. I need to put on a low dose chemotherapeutic drug right away, and my baby's pediatrician told me I need to stop breastfeeding if I take the medication. 
I'm pumping like crazy this couple days trying to save as much breastmilk as I could. My nipples start to getting very sore, but I just don't want to stop. 😔Â