I've found that usually the followup is dependent on you and your ongoing levels. It can change . You goal is to surpress your natural thyroid cells desire to make more cells by "tricking" it into thinking there are plenty of cells . I had blood tests monthly (not stopping medication) , the first year. Then did a uptake scan (during that stopping the thyroid hormone/medication ) and specific foods that could affect the test. Unfortunately in my case, i had to have another strong I131 treatment and I went right back on a suppressant dose. We opted to do another scan 1 yr later, and things were pretty stable. We discussed my options , as we were concerned about radiation levels, low red blood cell function and going off the surpressant dose was concerning , so we just monitored my blood levels for the next two years before a scan. Again, after that was somewhat similar and showing reduced uptake, I just monitored blood levels every 6 months after that. Thats my schedule for almost 30 yrs now! I'm now on a lower dose and things seem stable still!
It's all about balance. They have learned so much more in last years. I treasure each day... appreciate the time I have and do my blood tests consistently... make sure I schedule a reminder in my calendar so if Dr office doesn't order them ... I call them to get it scheduled. I also use pill holders that show me each day that I've taken meds, just to be certain I dont forget. I take throid in am, 2 hrs before food or coffee.
Good luck, hope all settles down for you .