How to boost confidence!!?

I have a very low self esteem. I think I'm ugly, I have had acne for 3 years (since freakin 5th grade!), I have a tummy, and I am always bagging on myself. I know I'm not fat. I'm 14 and I'm a double zero in pants and extra small and small in shirts. My friends are so pretty and it just makes me feel bad :( I want to feel good about myself. I feel like their compliments are pity.... Does anyone have any tips? And the whole saying I'm beautiful in the mirror doesn't work because then I look at myself and pick out every little imperfection.