Hello and welcome to healthcaremagic
Acne can affect the face as well as the back because these areas are rich in sebaceous glands.
For severe acne OR for acne unresponsive to traditional anti-acne medications,
Isotretinoin is the drug of choice. It the only drug which offers any chance of long term cure and after a full course of isotretinoin significant number of people never have a recurrence of there acne.
For you, in addition to Isotretinoin, I would suggest an
oral antibiotics as well, to bring down the flare/inflammatory papules/pustules. For inflammatory acne(papules and pustules) I usually advice my patients to start with
Azithromycin 500mg. The antibiotic can be continued for 4-12 weeks depending on the response.
In addition to oral retinoids and oral antibiotics you must also use topical antiacne remedies e.g
benzoyl peroxide gel OR Clindamycin+
nicotinamide gel (as you have been using already).
Since Acne and seborrheic dermatitis/dandruff are usually associated it is advisable to continue with an Anti-dandruff shampoo(as you are already using) since acne is worsened by dandruff.
regards