I had gone through your query and understood your concerns.
Hashimotos can cause hypothyroidism
and leading to serous cavity effusion.It can cause braethlessness and palpitation
mild pain .Get an chest xray P/A view and Lateral view to rule out pleural effusion
Hope this guides you. If you have additional questions or follow up queries then please do not hesitate in writing to us. I will be happy to answer your queries.
If you do not have any clarifications, you can please close the discussion and rate the answer. Thank you.
Wishing you good health