I got a call back from the ABA counselor She spoke to Jeanette Elliott who is their specialist when it comes to breastfeeding and IVF and pointed me to a section on the ABA website that had a podcast of Jeanette doing a talk on the topic. She even gave me Jeanette's phone number in case I still had questions!

The podcast was really good and answered a lot of questions for me. Am I allowed to post the link to it here?

The main points were:
~ Not all woman HAVE to give up breastfeeding
~ A woman whose menstrual cycle has returned regularly while still breastfeeding may not need to wean
~ Breastfeeding would least affect woman that are having FET's that don't require drugs
~ She went through each drug and talked about how effective it's transmission through breastmilk might be, and how to reduce the amount bub's might get. For example, drugs given by injection are probably given that way because they are less effective as oral drugs, therefore any that gets through the milk would be less effective than via injection, and also that the drug would first go through the baby's digestive system and get broken down more.
~ Most drugs are once daily drugs, so if you breastfed just before taking the drug, then wait as long as possible before feeding again it will lessen the amount in the breastmilk.
~ Many of the drugs used are found in a womans body at some stage in their menstrual cycle or pregnancy anyway (although usually at lower levels)
~ We need to balance the benefit of continuing breastfeeding vs the potential risk of the drugs.

Overall I was quite pleased with the info. I'm going to discuss it with my FS on Wed and see what he thinks. If he's not keen I'll even suggest that maybe I could feed DS before taking a drug, then express and dump the next lot, then go back to normal feeds...