Weaning/pump and dump question


My son is almost 13 months and we would like to try for #2. I do not want to wean him this early (wanted to go to at least 18 months) but in order to get pregnant again I need to take letrozole, which is not bf friendly. We are weaning him from day feedings now but the nights are hard. Would it be ok to pump this week to get enough milk to cover the 5 days I am on the pills, pump and dump the 5 days, then go back to breastfeeding? Update- I checked with the breastfeeding consultant. Letrozole has a 48hr halving time. This means that it will take at least 5 days to get out of the breastmilk after I finish the last pill. Letrozole can cause problems with bone, hormone, and sexual organ development if passed through the milk to baby.So I will definitely be weaning him.