You have two things to deal w/ patiently -- the natural shape of your legs (or equivalently your body's natural tendency to deposit fat & muscle) and your relationship with food.
Both come with time, patience & persistence. I understand the stress of wanting your body to be a certain way -- I think we all do. And as you've already experienced with the pills, crash diets, etc. there's no quicky solution to it. I'm more than 2x your age and I'm just now starting to get control of how to reshape my body, and its taken 23 yrs of training, 5 yrs of competition dieting and just getting more comfortable with myself.
I used to think I had "big" legs, a decent waistline, no boobs and a not spectacular upper body. (I'm talking when I was 19...) After running through my first bodybuilding competition where you basically diet down for the first time in your life and expose where your really tough spots are -- I found that I diet down fantastically on my waist, my back and upper body are great after yrs of lifting, and my legs are really nothing spectacular and most of the size I thought I had was really fat (or lack of muscle). Oh yea, and I could afford to buy my own boobs
That was 5 yrs ago. NOW, as I've entered into what one might call peri-menopause (at least I've noticed some changes that could only be due to hormone changes...) Now I carry all my fat in my waist. I just competed in another show and was able to whittle down most of my tuff spots but the waist is still an issue. I also think I'm too big in the upper body now and workign to cut that down or at least reshape it. But to do that I'm really looking at a couple cycles of training / diet that are focused on that. I'm not just trying to lose bodyfat, but rather reshaping my body. But that takes more than just one diet stint. And to both achieve this and maintain it, this means I need to be consistent and persistent with my diet & training. No quicky fixes here.
At your age, the best thing you can do is establish a solid & healthy diet - as you said you are only 19. You NEED to get a good diet established & follow it because in a sense you are still growing and your body really needs to be fed cleanly and correctly. You are in the prime of your life - your growth hormone levels are almost at their highest and that means your body WANTS to run as efficiently as it can. It can best do that with a clean diet and activity. USE your body so it can run efficiently.
Stay away from the fad diets & pills because you've already seen that they dont' work. Maybe change up your training if you've been on it awhile and results are stalling. I'd recommend breaking up into body parts instead of full body workouts. Time to start optimizing! And you will see results. But if you panic and start making yourself feel bad because God saw fit to give you big strong legs, then it won't get you anywhere. It is really a fight of mind over matter sometimes, but putting in the time and energy now will pay off before you know it and will stay with you for the rest of your life so you aren't sitting there at age 40 goign "holy shit I have fat thighs".