Monodox is given quite often for acne and works well. It's often seen that acne treatment is long and hence it's quite difficult to say why you are not responding to treatment.
Need to probe your history regarding menstrual history, use of other products, any other medical illness, acne lesion count etc. Sometimes if one drug doesn't work another group of medicines may work.
I would suggest you visit a dermatologist for further evaluation. Having said that I would suggest you keep in mind that acne and acne scars need a long term treatment spanning over months..
Dr Rashmi Soni Lohiya
(DNB, DDV )