First off there is nothing wrong with you. Humans function in a state of disease, in whatever form that may come in, addiction is part of who we are, good or bad. You are who you are, and you made the decisions that you did for a reason, and the only way to look is forward.
Speaking from the standpoint of just recently starting college 2 years ago, it's a lot harder to function on drugs as an adult compared to youth when you might have considerably less responsibilities, though I can't speak for your situation. I think it's great you are trying to get clean but you need to understand that you have significantly altered your brain at a key point in its development and it will be harder to quit and makes you prone to relapse and moving on to other drugs. Like I said, I can't speak for your situation, but generally this is true.
I think you need help, in whatever form that may be. Are you open with your family about your drug use? From personal experience that is the best route to take if it is possible, as hopefully they will understand and try to help you. You owe it to yourself to keep yourself healthy, you're about to enter a pretty important part in your life and you shouldn't make it any harder than it has to be. You don't deserve to suffer from this. Whoever you feel like now you will not feel like in a few more years, later.
You don't have to do drugs your whole life, I think you will find there are many other rewarding ways to spend your time...do you have any hobbies or dreams that drugs keep you away from? You should use those to motivate you and replace drugs. Long term gratification from creating art or succeeding in anything or playing a sport etc is more difficult to obtain but more rewarding than short term gratification from drugs, food, sex, etc. Not that those don't have a purpose, but when you let these vices consume you is when they are an issue because you don't make anything better out of your life with them! Drug addicts are wired towards short term pleasure so you will need to "exercise" your mind, if you will, towards being more productive, healthy and enjoyable things for your mind.
Also, exercise and meditation are great. Exercise naturally releases endorphins and can replace the "empty" feeling one might have when quitting due to a lack of chemical induced dopamine production. The poor health of an addict's body/mind is a great cause of suffering so you should do your best to take care of both and keep them healthy to aid in your recovery. Meditation is also a great practice for anyone, and I suggest you take it up as a more healthy coping mechanism, I think you will find a lot of benefit out of it. Remember, you're just human. The brain is a very...perplexing organ. We often have the illusion of control over it, but it really functions similar to other organs in your body, though quite different as well.
Anyway, all I'm trying to say is be patient with yourself and keep moving forward, work hard, and get help, open up to your loved ones and just know this will get better! I wish you the best of luck