I Have A Bottle Of Liothyronine Sodium 5mcg. On The

I have a bottle of Liothyronine Sodium 5mcg. On the pill there is the number 18. On the other side there is a greek letter. I think it is Epsilon. It looks like the letter e more or less. The greek letter is probably the company. But I think that instead of the 18 there should be 5. This is a new refill and I took it for the second day and now have palpitations. I know that this is sign of too much thyroid. Can it be that I received the wrong dose?