I think your case needs more investigation and you should follow-up with your endocrinologist
for this problem. Here are my reasons. First, I agree with your physicians initial thought that you had "subclinical hypothyroidism" because a high TSH is usually a more sensitive marker of hypothyroidism than the T3 and T4 levels. However, replacing your thyroid hormone did not bring your TSH down to normal and now you are having symptoms that could be due to hyperthyroidism. One possible way to explain this is if you have a hyper-functioning anterior pituitary gland in the brain that is abnormally secreting too much TSH. This would cause a high TSH and (usually) a high T3 and T4. This is actually a very rare problem, but possibly warranted in you. I would consider a brain MRI
if I was taking care of you. Most likely it will be normal, but at least that's off the table. Then what I would do is monitor your TSH and other levels very closely and try to get them all into normal limits probably by increasing your levothyroxine. You might also need to have a further workup for the cause of your fast heart rate and fatigue which can be due to other problems. Again, you should follow with your endocrinologist for this problem. Good luck.