Losing weight once and for all!!! (Hopefully haha)

Hi everyone, I've been trying to lose weight for sooo long! But it just seems to keep creeping on. This time I've decided I HAVE to do something about it and lose weight once and for all (though I say that everytime, I hope this time it will really work) My weight has got to the point where it has really started to affect my life!
I've only just turned 18, I'm supposed to be out having fun with my friends and being care free but instead I feel too self conscious of my weight! I'm not enourmously over weight, but I need to lose 2 stone to be classed as 'healthy'. It really doesn't help that all my family and friends are slim because they're constantly telling me 'just excercie more and eat less' but they don't realise how hard I try, I've cut down on so much food and try to run everyday with still no change. Whereas they can eat whatever they want and do no excercise and still stay slim, which is unbelievably annoying!! My Mum thinks that I may have an under active thryoid as I have all the symptoms including weight gain, though to be diagnosed I need to have a blood test, which (I know it sounds stupid) but....I have a MASSIVE phobia of, I've tried so many times but I literally faint and become really distressed. I just can't bring myself to do it. Anyway....I REALLY hope that I can lose some weight and ideally be officilally classed as HEALTHY!!! Also, prom's coming up and then university so it would be amazing to look half decent for that! I've thought that I've always been fat but when I look back on pictures (even from only a year or two ago) I can see how much slimmer I was which highlights the fact that I must be gaining weight!! It's weird that I just don't notice it?! I've tried diet pill, going to the gym, running, walking ...etc but when I notice no change what so ever it's hard not to be discouraged so sooner or later I end up giving up
Pleasee lets try and do this!!!!