Hi!
Well, you want to reduce about 75 pounds in 7 months. That is not a reasonably easy target, about 10 pounds a month. It would be best to lose about 5-6 pounds a month and tone up your body. This way also you will be in a great shape for your holiday.
If you want to lose weight, then common causes of weight gain like overeating, lack of exercise, diabetes, hypothyroidism have to be ruled out in your case. You must then look for other causes. One is water retention due to low serum protein. This along with anemia can cause unexplained weight gain. Adrenal gland problems are the other cause. Cushing’s syndrome should be looked for. The kidney function too should be assessed. Late night snacking and poor sleep too can cause weight gain. Polycystic ovary too causes weight gain, hence has to be ruled out by an ultrasound of abdomen. Certain medications like antidepressants cause weight gain.
If all these causes are ruled out then you can start a diet and exercise program to lose weight. If you want to lose weight, then you must do it the scientific way for long term benefits, healthy glow, and a good physique and body. It's best to join a nutrition expert and a physical trainer and follow their advice. Incorporating yoga into this regimen takes stress out of this exercise to lose weight. Also the diet should contain more of green leafy vegetables, fruits and protein and less of spaghetti, potato etc. I suggest you eat frequent small meals and stop counting calories. It is best to eat lots of fruits and non-starchy green veggies, go slow on fats, eat carbohydrates in moderation and increase your protein intake (lean cuts, whites of eggs etc). Drink plenty of water and non fattening fluids such as clear soups etc. Look for hidden calories in salads and soups and avoid them (eg: cheese, butter, dressings etc).
Also, you need to exercise regularly. A combination of aerobic, strength training and stretches works best. Many people find it difficult to fit an exercise regimen into their lives. The best way is to join a gym. If that is not possible, try building exercise into your daily life. If you lead a busy life, then walk to work, or to bus stand etc, climb stairs instead of using lifts, walk while talking on cell phone, or briskly walk to any place you are going to. See how you can change your lifestyle to incorporate exercise. Hope this helps. Take care!