hi and welcome to HCM
Firstly the skin colour can change as you age as sun exposure increases, also
hormonal changes can increase the pigment in your skin.
Similarly with acne, it may happen till your early twenties,esp around your periods.
But don't worry, firstly to treat the acne, use Deriva -CMS at night only on the pimples and marks. Take a course of doxycycline tabs for 2 weeks to control the infection. The cream can be continued.
Use a facewash such as AHA glow or Glogeous which will help your acne as well as complexion.
Most importantly always use a sunscreen whenever you step out even for short duration. Use a gel or water based one for your skin.
For under eye circles use
kojic acid gel. It will take a while to show improvement.
You can later
consult a dermatologist regarding other options for scars and skin lightening like
chemical peels,
dermabrasion, lasers. etc once the acne is in control.
Remember to eat healthy, drink lots of fluids and avoid long hours in front of computer, late sleeping.
Hope this helps.