Hi Bo
Sorry to hear you are feeling so down - I really know how that feels. I was diagnosed as desperately under active (hashimoto's thyroiditis) when my baby was around 3 mths old. My condition had got so bad that my body 'had just about given up' (according to the consultant.), and I thought I was cracking up, I was so weak! Please show this to your husband if it helps him understand that you really are ill. On the brighter side, once the medication kicked in, I now feel much better, but this is not overnight.
One slight concern is that you described your diagnosis as being overactive, but you seem to have the symptoms of an underactive thyroid(lethargy and the weight thing). I actually gained around 1 1/2 stone in weight after my baby was born, which was down to the thyroid problem. Sorry to get technical here, but is it your TSH level which is high? This means that your thyroid is under active - might be worth a discussion with the doc. Are you having treatment? If you have concerns, hassle your GP - I had to ask for the thyroid test myself which led to my diagnosis. Its really difficult to do when you feel so low, but trust me, you need to.
I really hope that you get the treatment you need - I was lucky to get referred to a consultant at our hospital, and I am now monitored every three months. All I can tell you is that you are not going mad (even though it seems that way when you are going through it!), and it will get better.
Also, I breastfed my daughter for three months after starting my treatment (artificial thyroxine 100mcg/day). No-one mentioned the possibility of any adverse reactions in the baby, but she was also tested for her thyroid levels, which were ok.
Sorry to have waffled on a bit, but I hope that I have at least helped you to believe that it will get better. You have to be strong and believe that, and you will get through. Good luck.