I'm probably going to say the obvious now, but... There are a lot of causes of dull skin, but these are the most common: not enough exfoliating, the air and atmosphere that you are in every day, stress, your diet and not drinking enough water and of course using the wrong products.
And what about pimples? When it comes to clear skin, pay attention to what you put on your face - like cleansers, moisturizers, and makeup - and what you don't - like unwanted bacteria from your fingers or dirty brushes and sponges. If you've tried so many things and nothing works, make an appointment with a dermatologist. They may prescribe treatments like antibiotics or prescription medications to help clear your skin.