The acne could have been brought on by a variety of things such as diet, stress, hormones, oily skin etc, so it can sometimes be hard to pin-point exactly why it flared up so suddenly. I'd suggest looking at your diet first. Do you have a lot of dairy products? They can usually be one of the reasons people get sudden breakouts.

There are a ton of methods you could try to help clear your acne, but they are really all just trial and error products. You can get various spot-treatments with salicylic acid from stores or buy acne sets such as Proactive, Burt's Bees, Clinique etc. While these methods can definetely work for some people, going to a dermatologist would probably be the best choice as they can help identify what's the main cause of your acne and help perscribe products based on what they think is causing it. They can give you topical products with a higher amounts of benzoyl peroxide and other acne-fighting ingredients, antibiotics, or (if they believe it's necessary) accutane. Of course there is always the natural route that can work just as well as a product given to you by a dermatologist. You could try applying apple cider vinegar topically and leaving to dry overnight (or you could try with salt water), using lemon juice topically, drinking green tea (helps balance hormones), making egg white masks, and making honey masks. There are tons of home rememdies available that help target acne.