I Have A Low Thyroid Problem And Have Taken Thyroid

I have a low thyroid problem and have taken thyroid medicine most of my life. In the past I took Sythroid, but CVS switched it to Levothroxine. In the last three or four years, I have lost all the hair on my legs and most of the hair under my arms and the hair on my head has thinned excessively. My fingernails are a mess. They chip, delaminated, and crack. Is this cause by the generic Levothroxine as oppose to Synthroid? I am 76.