he kept telling me that God doesn't make mistakes and that I had to stop looking at myself as a mistake
True. God doesn't make mistakes. You aren't a mistake. You're a human: we all have defects. Nobody is perfect.
if I'm not a mistake then he did this to me on purpose, so what it is
You may not like this: God doesn't owe you an explanation, and neither do you have to know "why" something happened to you in order to be grateful for the life He gave you.
I'm going to try and find someone who will listen to this whole story, try to make some sense out of it, and help me with some real world techniques to deal with the absolute anger and rage issue I have over this
Basic: The reason you have anger/rage issues is because things are not going in the way you would like to. Even when your favorite football loses you can experience anger. So, how do you deal with it? Be realistic: things won't always happen in the way you want them to happen.
My advice (not a doctor. Just basic stuff):
Recognize you have a problem (Gynecomastia) that won't go away without a surgery. You won't fix it by getting angry. Then, decide whether you are one of the people who want to get rid of their Gynecomastia, or one of those who have no problem living with it.
If you're the latter, then that's it. Go and live your life.
If you're the former, then make "Getting rid of my gynecomastia" your decision, your goal. First, find out the cost of Gynecomastia surgery in your town. If you don't have the money, work hard, and save money until you get enough for your surgery and some meds. Because this kind of surgery is expensive and most health insurance companies won't pay for it, it will take you time to get the money you need.
During the time you're working towards achieving your goal (Getting rid of Gynecomastia), you may get depressed, angry at God, angry with others, discouraged, etc. But, hang in there, remember you took a decision, you set a goal, and since you're a man who keeps his word, you have to do it.
So, it's essential that you have realistic expectations: this will take you time and will cost you money. You may not like the life you have had, but if you can do something to fix it, and want to fix it, go ahead and do it.
Some people not only don't like the life they have, but they can't do anything to fix it, to get rid of their problems. I was going to post here some examples of what I consider real health problems, but then I remembered that I don't think it's good to compare your situation to that of others in order to feel "better". Just be humble, accept the life you have and, if you can do something to fix it, go ahead and do it.