What Causes Dizziness And Headaches While On Synthroid?

Hello, I ve been on synthorid for the last 7 years. 75 mg. Yesterday my doctor increased my dosage to 100mg after a blood work that showed TSH at 4.760. Do you agree/ I ve been feeling bad lately, with some dizzines, headaches, arritmia, etc, not sure if related to the thyroid or not. I m a male, 46 yeats old, not overweight. Thanks!