Could my acne treatment just stop working?

right before christmas break i went to the doctor for acne treatment because it was getting really bad. he gave me a prescription for clindamycin phosphate pads to use twice a day and said it would take about 6 to 8 weeks to fully take effect. at first it was working great and gradually getting better every week, but for the last two or three weeks my acne has just kind of been stable, but my skin is nowhere close to being clear. is it possible that my acne treatment has stopped working? should i go back and get a different treatment?