Hello and welcome to healthcaremagic.
Acne if moderately severe, need to be managed with both topical as well as oral medicines, specially since your acne has not responded adequately to topical treatment(
clindamycin gel), inspite of using it for 3 weeks
-Oral Antibiotics: For inflammatory acne(papules and pustules) i advice my patients to start with one of the oral antibiotics leither Azithromycin/ Doxycycline OR
Minocycline.
-Topical treatment: Is a valuable adjunct to any form of acne treatment. Mainly two classes of drugs are used topically
Topical Antibacterials: Either clindamycin 1%/
benzoyl peroxide 2.5% OR
Nadifloxacin during the day time.
Topical Retinoids: Either
Adapalene 0.1%/ Tretinoin 0.025% OR Azaleic acid (10%/20%) at bed time.
I would suggest addition of an oral antibiotic e.g doxycycline or azithromycin, for a few weeks as well as topical benzoyl peroxide gel for night time application, in addition to topical clindamycin phosphate gel that you can use during day time.
regards