The first thing to do is to get your thyroid function checked by a physician who knows the proper tests to use. There are other disorders that can produce the signs and symptoms you mention, and you don't want to medicate with anything until you know what the problem is.

I would steer clear of animal thyroid for two reasons - variability of dose due to not having standardized preparations, and also risk of infection. Some companies sell bovine thyroid from god knows where (domestic sources? India? China?), and I'd be queasy about mad cow disease and other potential problems.