High T3 only

Less than a year ago, I was diagnosed with Hypothyroidism,
2 thyroid nodules and 1 enlarged lymph node in my neck. I am
taking Synthroid, and the hypothyroid seems to be controlled,
but now other numbers are off, especially my T3 numbers are
high but not T4. I was told that T3/T4 usually follow each other. I am scheduled to see an endocrinologist, soon. But, I
wondered if anyone else has been told this, and what might be
the cause. I was treated three years ago for stage III breast cancer chemo/radiation and I wondered if that can cause
my bloodwork numbers to be all over the place.