Every morning at 5-6am my heart starts pounding & can't get back to sleep. once i am up i am fine. just increased thyroid 6 weeks but tsh is still high.

Poss. Sleep apnea: I would recommend that you see your family doctor and get a consultation with a sleep disorder specialist. You're having a definite change in your cardiac status in the morning. Sleep apnea occurs most commonly during rem sleep, and this occurs mostly early in the morning and can cause cardiac arrhythmias.

Need evaluation: Your hypothyroidism appears to be inadequately managed. Are you overweight. You may what your md to ensure you hypothyroidism is well managed and evaluate for sleep habits and disorder.