answer:  I cannot tell you to go against your medical doctors advice. However, what I can tell you is to do the research first. I have found that most doctors, out of fear and not knowing and the lack of desire to nourish the ever important breastfeeding relationship, often tell women to stop  nursing. However, the impact that will have on a young baby physically and emotionally , unless by dire need, would be too much in my opinion. So... what I suggest you do, is get the name of the medication he is trying to prescribe and go to www.safefetus.com and do a drug search. It is a website that gives much information about drugs pertaining specifically to babies and nursing. if you are able to take it during pregnancy, you can absolutely take it while nursing.  You can also obtain a copy of dr.Hales medication and breastfeeding books. Every couple years he updates the book of every common medication that out there and gives stats on how it effects breastmilk and babies . I would do this research and take this to your doctor. and show him you did your homework. I would also contact a couple lactation consultants in your area and have them look it up as they have more medical training than i do as a doula and breastfeeding counselor. But if you take the information you get from all those places , and you get consistently that it is ok to take these meds or to not, then you will be more clear in your decision. You can also look into if there is another medication that can do the same thing but isn't as risky during breastfeeding. This you can ask to an LC also. Find out alternatives. Ask your doctor what  are the pros and cons of not taking more of this medication. and weigh them to weaning a baby who would thrive best on breastmilk and the nurturing it provides.  It seems as though it is ultimately your choice, as it should be. Do the research, find answers to bring your own clarity. Maybe it wont be such a bad thing to wait 6 months, test your thyroid again in a few months and see if anything has changed... put it off as long as you can... be creative so that you and your baby get the best start to this relationship and life together as you can. If your life is in jeopardy its a different situation. all questions to ponder... I hope that helped! if you have followups please let me know!~