I'm sorry. I had a similar experience and diagnosis several months ago. I had insomnia, heart palpitations and weight loss that couldn't be explained by BFing. Turns out mine was hyperthyroid and Hashimotos, not Graves. My doc and his thyroid specialists chose to wait it out and see if they hyper resolved itself (by killing the thyroid) as it does in most postpartum women who develop it. I was put on heart meds for the palpitations and said to not get pg and come back for more bloodwork in a few weeks/months. It's still on my to do list.
I hesitated to do anything more, because either option requires me to stop breastfeeding and I wasn't (and am not) ready to do that.
Best of luck in getting on the road to feeing better.