Curious About How Bad Side Effects Are

I just got synthroid today and haven't taken it yet. Are side effects more common than not with this medicine? I also take valium at nite and I take Lortab. I also take high blood pressure medicine. I have a kidney disease and blood disorder among other things and something new they can't figure out. I have had several blood transfusions and iron iv treatments 20 days in a row, my body is attacking itself, but not bleeding internally. I am worried about the side effects, itching, not sleeping, nervousness,etc. I have lost weight and I NEED to gain weight. does everyone gain with this medicine, we can't figure out why i keep losing and i only weigh 105 now. thanks. i hope i can figure out where to go to find answers.......