I've had Hypothyroid since I was 8, and learned to feel when my synthesis needed to be increased. Since being diagnosed with Mg 3 years ago, those signs have faded away. I just had my levels checked and definately needed an increase. Since about 2 weeks on my new dose I've had much more energy (not more strength). People with the "normal" Tsh levels are wide 2-8 I believe. My body only runs normal on the very very low side of that spectrum. So find out what the levels you are at. Maybe you aren't on a high enough dose to notice a difference? Also, I get a bit jittery and have slight palpitations with every increase to my thyroid dose. They subside around the same time it kicks in.
One other symptom I've always had when I'm too low on my meds... Carbohydrate cravings (extreme) and when I'm normal, my hunger and cravings are much much more moderate and normal. Also long term thyroid will cause dry brittle hair. So if you notice your hair is suddenly very dry and frizzy it's time to get checked!
I hope this helps and finds you string and well.
Jess