Yes, I think that’s a very good idea to check back with your doctor about these new symptoms. If the Hydroxyurea you were taking for ET was working for you without any side effects you might want to consider returning to that medication. Many people have been on that drug for years because it works so well. The risk of developing leukemia is very low and the benefits of the drug outweigh those risks.

Something to consider. This switch to Peg-interferon may have brought on the increased issues with your thyroid and possibly causing some of your other symptoms as well, since they seem to have started with the change in meds. These symptoms are tangible and creating obvious issues, while the threat of leukemia from the hydroxy was only in the fine print and minimal at best. This would be a good discussion to have with your hematologist and your general practitioner.
I hope you were able to enjoy your vacation. ☺️ Will you let me know what you find out from your doctor, please?