I am 57 years old and have been on synthroid for about 3 1/2 year...

I am 57 years old and have been on synthroid for about 3 1/2 years. I had a nodule on my right side that was removed.I felt great but was told to see the endocrinologist. I felt better for quite a while but NOW I have gained over 25 pounds, out of breathe just going up stairs and feel like I always have a lump in my throat. The weight gain has made my feet, back and knees hurt. I have been exercising and even did Jenny Craig and only lost 10 pounds just to put it back on. I retain fluid in my hands and legs. Sometimes my legs feel like they are going to burst. I am seeing many of the same complaints on this site about synthroid. What is this Armour people are talking about?