Acne resulting from Levothyroxine

I definitely know the acne i'm suffering from are the results of Levothyroxine i'm taking desperately. recently i'm taking Tetracycline capsule 250 every 12 hours and i can look at the mirror confidently again. but how long should i take this capsule? and as swallowing the capsule for a long run, is it possible for my body to be resistance toward this and it wouldn't affect the acne????