What Causes Palpitations And Insomnia After Increase In Synthroid Dose?

My doctor increased my synthroid dose for hypothyroidism from 110mcg to 126mcg. After 3 weeks, I am having heart palpitations, neck and muscle pain, insomnia, diarrhea, breathlessness, and fatigue. My friend had similar symptoms when she was struggling with hyperthyroidism. I called and asked if I am taking too high a dose and they said my levels are all normal (They took t3 and t4 tests, also) They suggest something else is wrong with me. Are they right or should I look for a second opinion?