I've had thyroid cancer and I wasn't tired at all. However, having an underactive thyroid can definitely make you tired so is it possible your thyroid is underactive? I think thyroid cancer can coincide with thyroid function problems.

I also wouldn't worry about the stage. If you are having difficulty taking care of your girls, you need help, whether it is because of the cancer, your cold, stress or whatever. While thyroid cancer is a comparatively mild form of cancer (compared to some other forms), it is still pretty massive news and I am sure your family don't mind helping.

I will add that I was back at work a month after my operation. It may or may not be the same for you. I am just saying this so you don't feel this is something that is going on forever. You may well feel completely back to normal in a month or six weeks. It will depend too on how quickly you adjust to the medication. Some people apparently have difficulties with it. I didn't. I think most don't. 

Feel free to ask, either here or by messaging me if you want to know any more about my experience. Yours might be different of course, but it can be helpful to hear somebody's experience.