Help with my pimples?

Doxycycline works well for about half the people who use it. For the other half it works poorly, or not at all. The basic problem is antibiotic resistance. In the US and Europe, the bacteria that are responsible for acne vulgaris infections, P. acnes, are becoming more and more resistant to commonly used anti-acne antibiotics. Specifically, tetracycline antibiotics (minocycline and doxycycline) and macrolide antibiotics (erythromycin, azithromycin and clindamycin) have high rates of resistance. If your skin is colonized by a strain of P. acnes that is resistant to a particular antibiotic, then using that antibiotic is not going to help much. Fortunately, there are lots of additional options for treatment. But it seems like your dermatologist is kind of stringing you along. Most succesful antiobiotic treatments should start producing significant results within 2-3 weeks. Not 2-3 months.