Levothyroxin causing weight gain?

So since taking levothyroxin I have noticed some positive changes like my hair stopped falling out. But I have gained 70 pounds and now I have high cholesterol even though I eat healthy and exercise.. The only difference in my life is that I take this medication. I recently learned that when our body converts T4 to T3 sometimes it converts it to reverse (rT3) instead and this could cause weight gain and other symptoms does anyone else know anything about this?