re getting too much T3 is to have free T3 (FT3) tested regularly.
Too much T3 usually causes hyperthyroid symptoms (anxiety,
weight loss, insomnia, heart palpitations or tachycardia, intolerance to heat. etc. - although these can vary). T3 is about four times more powerful than T4, so it can also get you into trouble that much faster. When on a T3 med, it's doubly important to test FT3 along with FT4 and TSH.