I will recommend you to read a lot on this forum, as you might will get all of your questions about acne answered. You should maybe conisder starting on the regimen? You can go to your doctor and see what he/shee will recommend for you. If nothing helps, antiobiotics, gels etc. then you should really consider going on accutane.

For red marks/scars, theres a whole room for this. GL

Your story sounds like me when I was 15. Don't worry, acne is very common at your age due to hormonal changes. I also have oily acne prone skin. I recommend getting a gentle cleanser, I started with cetaphil. I would also pick up a gel that contains benzyl peroxide, I have one from CVS that is called CVS acne gel. Clean and Clear also has a benzyl peroxide gel. After that I would use a moisturizer, one with SPF is great especially if you are outdoors. Also try to incorporate skin foods to your daily eating routine. Greens and fruits are great. Grapefruit is great for the skin, and green tea has lots of benefits as well. As far as dark marks if you want a natural way try using a fresh lemon and squeeze the juice out. Dab it onto a cotton pad and put it on the affected areas. I do this and it works well for me! You can rinse it off after 20 minutes or leave it on longer. I personally leave it over night sometimes. It may sting a little at first but it goes down after a minute or so! Stay Positive:)