Acne returning, need some insight?

For about 3 years now ive had really bad acne, i had tried proactive and that did nothing for me so i went to the doctor and she prescribed to me Apo-Minocycline pills and a cream. After about 2 weeks i immediately noticed a difference and my face was almost completly free of acne. About a week ago i started to get 1-2 zits back but now it seems like it is all coming back...im still taking the medicine and using the cream daily but im wondering why this is happening.