Often, not ofteh. :) I would call more than one RE's office to ask what donor-egg agency they use.
The things in your favor, incidentally, are your height and your youth. Some RE's won't let their women using donor eggs use eggs from women much over 21 or 22, in order to try to guarantee the best results. So ask your questions and get ready, so as to begin donating as soon as the good agencies will put you on their list.
There are a lot of good donor-egg agencies that can answer all your questions. The money is good, the psychological hurdle does exist (a lot of women can't get past the idea that someone else would be raising "their" baby). I've met my donor, and she told me that the way she got around that worry was realizing that people using donor egg would be the most motivated parents of all, since they had been trying so hard for so long to get pregnant and had gone through so many failures.
I think that few agencies would deal with a teenager. Certainly none will use your services until you are 18, and it is possible that a lot of agencies would ask you to wait to donate until you are 21.
Regarding your weight, a lot of women who are in the position of choosing a donor do so with the idea of picking someone who looks similar to themself, and you are not the only person in the world with a weight problem. That said, if a woman gets to the point where she has to decide to use someone else's eggs, it is a sad day for her, and one way she might cheer herself up is to pick someone like her but who in some way physically or intellectually is an improvement. I picked someone who looked like me and had a similar ethnic background, but who was 2 inches taller. (I would have liked to be taller myself.) So you might find that some women would pass you by, since especially if they fight a weight issue, they might want to produce a child who does not.
If you have a lovely face, though it probably sounds cold to say it, you will also find that more people interested in using your eggs. The donor agencies list is sort of like a cross between a medical site and a dating agency, and people look at your photo and pick. If all else were equal, you would probably get more hits on a donor site if you could manage to get your weight to come down. But that does not mean you would get no interest otherwise.
Try a higher fat and lower carbs diet, that can help a lot if someone has gotten stuck when doing it the low-fat way. And try Weight Watchers. You can find your more reputable agencies with whom to sign up by calling the local well-respected Reproductive Endocrinologist's office and asking who they use the most ofteh.