You need a TSH, Free T3, Free T4, TSI, TRAb, TPOAb, and TGAb run. These will give you a full thyroid blood profile and you will know if the issue is autoimmune in nature triggered by your recent pregnancy.
I suspect that your GP said Graves because this is a sudden onset issue that has arisen since your pregnancy. Your symptoms are all hyperthyroid in character.
You also should get your Endo to run an ultrasound. He may want to to a RAI Uptake scan, but you might want to hold off until you are done breast feeding and your baby is older. DO NOT LET THE ENDO OFF with out at least ordeing that complete blood panel. If your issues are autoimmune Graves or Hashimoto's they can affect you, your child, and any future pregnancies. There is a genetic dominance in the AI thyroid issues.
Look over these threads of mine. They might help you enter your MDs appointment better informed and able to argue your case.
These are my general thyroid care and concerns posts... the cover how to look at your results and where you want to be.. etc: Thyroid care concerns around the world - week 2 Thyroid care concerns around the world - week 3
These are the threads that discussed my MD specialist information on thyroid issues and pregnancy: My MFMs Facts and Myths on hypoT/Hashimoto's pregnancies.
Hope this gets to you in time and that you have a good Endo.