Hi Prags,
This is sounds so concerning! Aside from the stroke, I am experiencing similar symptoms (Right Lobectomy and isthmus-ectomy in July 2022). I was diagnosed with Hurthle cell Carcinoma and am trying to get regulated on Synthroid too….it is a very weird balancing act because the issues seem to come and go for unknown reasons! Although I never really had allergies, I realize the allergy season could be adding to the symptoms….its hard to tease out normal issues with “signs of cancer.”
I am finding that the thyroid really is a tricky organ and Synthroid dosages are VERY tricky! When I was on higher doses of Synthroid I felt terrible! My doctor at the time seemed to think I should keep increasing my dose even when my TSH was low (50mcg 5x per week and 75 mcg 2x per week). I had to change endocrinologist due to the doctor not listening to me…..every time I took the increased dose I felt very bad for a few days. The new doctor lowered the dose again (50 mcg) and he is trying to see if I can keep my TSH level in the same range as it was before I was diagnosed (I did not have any issues with my thyroid functioning….I just had a BIG nodule)….I just started this so we will see.
So far, it has been difficult. Although I feel better than I did on the higher dose (a lot of the extreme symptoms are gone i.e., nausea, insomnia, and extreme sweating.), I still have symptoms similar to the ones you are describing, so I am concerned it is cancer again. It is hard to know what is related to cancer, side effects of Synthroid or another normal issue (Allergy, cold, reflux, etc.)
One thing that could be contributing to your symptoms is reflux. I have a history of stomach issues and the reflux is worse since I had the surgery…..I assume the big nodule in my thyroid was holding back some of the reflux from traveling as far up into my throat and nasal passages (haha). Coughs, throat pain, nose congestion, chest pain can all be associated with stomach issues and reflux, so don’t worry. It can also be associated with allergies.

I am concerned that my symptoms might be the return of cancer too, however I thought I would share some of the information that I have experienced in case it helps you. I am hopeful that your tests go well.
Good Luck!