stop taking synthroid, otherwise you'll be taking it for the rest of your life. I use to take it, but had similar problems. I now take Black Maca Extract and it's provided me with the effects i was looking for with synthroid. It's a natural product and I haven't had any side effects and am amazed how much energy I have and my concentration problems are now non-existent.
I had the symptoms you named plus hair falling out, restless sleep, tired all the time, etc. UNTIL I switched to ARMOUR for my thyroid! All of the bad stuff disappeared! You should feel better not worse on your meds. If I were you I would get on the internet and so some research on the other remedies that are available & work better for many people. It is worth checking into!
I was on Synthroid a few years back and experienced what you are plus loss of hair, weight gain, restless sleep, etc. I switched to ARMOUR and felt better pretty quickly. (At first my heart raced a little as my body adjusted to the new metabolism but isn't that what we need?)
I suggest you get on the internet and research the remedies that contain T3 as well as T4- you won't believe what you will find out! I looked up side effects and benefits of each remedy and then made a decision. Good lunck, Kathy