Skin problem. What to do?

Well first and foremost you need to apply a sunscreen everyday, 3 times a day even when you're indoors. That prevents ageing and pigmentation. What's happening is a vicious cycle of pimples which are leaving marks (post inflammatory hyperpigmentation). So getting acne under control is important. For pigmentation and dullness, there are variety of options, like Peels and Q switched lasers. You'll need 4-6 sessions of either. For under eye darks circles, you have to stop rubbing your eye if you do. Most times it's the hollowness under your eyes that appears like pigmentation but it is actually the vessels underneath throwing a bluish/slate brown effect called Tyndall effect, for which you'll need an under eye filler which will make you look significantly better.

Visit a dermatologist.