The thing about the age 14 is that it has quite weird effects on girls and guys. The guys, who are a little behind the girls in their development, have gone hormone crazy and started looking at guys properly in a more sexual way. However they are still immature at heart and therefore they are going to be superficial (again the sex hormones, looking for a mate with good genes) and arrogant (they are going to push away and play hard to get with anyone under their superficial standard). Girls can be worse as they go a bit insane too, but there are also trying to fight off the competition for guys, but at 14 they have no clue how to do it (hence your friend's reactions with your crush). That is talking about it in a basic and biological sense.
You say you are overweight. Never mind anyone else opinion but it is bad for your health and the fact you are going to weight watchers is a good start. But remember you don't have to be a stick to pull guys, just get yourself to a healthy weight you are happier and comfortable. And if you buy some flattering clothes (Im not necessarily talking about revealing clothes, just clothes that fit and emphasise your good points.) It all makes you more confident.
Confidence is very sexy. I think what you need to do is change your mindset. Rather than thinking, I can't get a guy because Im overweight, think I haven't got a guy because Im too good for them, and as long as you dont voice this, just show it in your body language and think it, it will make you more attractive.
I remember at school my best friend used to be curvier than other girls and not exactly wasn't incredibly pretty, but what she did was she played the game of guys like "they were lucky to have her" and had a lot of confidence thus. If a guy displeased her she would ditch him, her attitude? They weren't good enough. It was never "maybe it was my fault" it was always their fault in her mindset. And its the same principle with these guys. That guy who bends over to get away? What a loser! They aren't good enough for you! You are probably so beautiful as a person in many ways and they are just being blind. Also my friend, had more dates than any of my other friends who were slimmer and prettier!
When it comes to talking to guys, and anything else that requires confidence, acting confident is often the way to become confident. Its like theatre, when I began acting, I was frightened as hell to go on stage. And I made some big mess ups through that. But what I kept doing was going up and trying again and again until it the stage became less frightening to me. Its the same with guys, just keep going up to talk to guys about ANYTHING. It doesn't even have to be flirting. If you mess up, just laugh it off, its all experience and you will get over it.
Education is very important, maybe you should hold off this for a couple of weeks and then have a go at this. Also the summer is a good time for reinvention, so maybe your best bet is to ride out the next few weeks, study hard, lose some weight and go shopping and put these guys out of your mind. Showing that you don't need them (like my friend did) they may come to you and seeing that you are elusive and focused on something else.
A few things to have a go at, I hope this helps. xx