Well, I'm 19 too and I've been getting them since I was about 16. I have to say that I feel a lot better now but at the beginning I felt all the things you were describing, I especially felt light headed - like I wasn't actually there. I would say that you should go back to the Doctors again, be persistant until they offer you help. It's difficult for people who have never had a panic attack to understand how horrible and scarey they are and believe me, I've had people look at me like I'm completely and utterly crazy but at the end of the day, you can't help what you're scared of. I developed a phobia of fainting and therefore, hated to be in a crowded places, get too hot, not eat, stand up for too long etc. All of those things would set me off. I think when you have a panic attack it knocks your confidence which is what gives you the low mood, depression and anxiety often come hand in hand and it's so easy to just give up but the thing that got me through it was keeping busy. For about a year I just sat at home worrying and then wondered why I wasn't feeling better. I felt so low that I just couldn't be bothered to move and when I did I just felt dizzy and uncomfortable but then I started a course and went out every day, since then I have so much more energy and I feel like the fogginess in my brain has lifted a lot. So my advice would be just to keep busy, do things that scare you because once you've done them you have these achievements that you can use to prove to yourself that you're not useless or hopeless and you can cope with whatever's thrown in your direction.
Also, it's so common to worry about having a heart attack or something similiar when having an attack so they way I cope with it is to think that I've had a panic attack before and nothing's happened so why should it this time? A panic attack never changes, your body will always react in the same way and do the same thing.
Don't try and cope alone either, as well as talking to a medical proffesional, also make sure you confide in people you can trust and rely on as a good support network really helps.
Hope this is helpful!