I would speak to my doc first, and make sure I am healthy to do this. Now step two. You want to lose weight quickly, and as was pointed out, crash diets are not exactly good for you and don’t last the long-term. HOWEVER, I went on the Atkins diet a number of years ago before a simcha, and despite the criticism it has received, for a crash diet it is excellent. I lost weight quickly and felt very full, because you primarily eat low carb-high fiber vegetables and protein. I lived on salads and tuna or chicken, a little meat, eggs cheese, etc. No fruit until after the first two weeks, and then only low-carb fruits like blueberries, and a little cantaloupe.
For a short-term solution only, this is great (so is the South Beach Diet, btw, but it is a slower process). Drink water, but not to excess – there is such a thing as water intoxication. I would drink a glass before eating, and a glass after, with a few through the day. The water is necessary anyway, but especially when you cut your carbs. Read the labels on food containers, to see both calorie and carb counts, as well as fat, though some fat is necessary in ALL diets (use olive or canola oil on salads). Get lots of exercise walking – it really helps.
After you get off those first ten lbs, balance your diet with more veggies and a little fruit and (SOME)nuts like almonds and walnuts which are so healthy for us. You will lose weight more slowly at this point, but it is much healthier in the long term.
Please be realistic about your need to lose weight. If you are not a size 2 – so what??? But if you are 5’2′ and already a size 10/12, it is possible you could stand to lose 10-15 lbs. People mean well when they say you should look for a boy who is NOT looking for a dress size, but reality is that looks do matter to people, to some extent. Guys generally are conditioned to be attracted to the slimmer girl (or guy). In my opinion, while giving Gemarah shmoozes, the rebbeim should be teaching their bochurim to be less shallow. the Shadchanim should be doing the same, especially with the boys’ mothers.
Be confident in your personality and charm. The number on the scale is only ONE facet of what makes you YOU. Hatzlacha rabbah.