There is no way to get rid of Acne in 3 weeks. All Acne treatments start toward at around 3–4 weeks and will reach their maximal benefit in 2–3 months.
You can - nevertheless have some improvement in your Acne with the right daily routine. It is crucial to take seriously all Acne prevention tips (i.e.; right cosmetics, oil free makeup.), change your diet according to recent Acne advice (i.e.; reduce intake of cow milk and dairy…) and of course start treatment based on your Acne severity.
Among all available treatments, blue light phototherapy maybe the fastest acting. Combining it with prevention, topical and oral treatment may result in quicker skin improvement.