Simple answer -- if the only lifestyle change you made was adding in exercise, the weight is almost certainly muscle. While this may initially be discouraging, muscle tissue increases your body's ability to burn calories, so this is a really good thing.
Next -- 35 pounds in 15 weeks, especially if it's your last 35 pounds, is pretty unrealistic. Some people can lose as much as two pounds a week when they're losing it in a healthy way, but the last ones are the most difficult to lose. It took a long time to put on, and it will take a long time to take off. Generally, a loss of about a pound a week is reasonable.
My very best advice for lowering the calories is to add in more fresh fruits and vegetables, and drink more water. Produce is really low on calories but high in nutrients, water not only flushes toxins but also helps you feel fuller so you don't feel like eating as much. The USDA recommends that your diet should consist of roughly half fruits and vegetables, 1/4th grains (and half of them need to be whole grains), and the remainder split between meats/starches/legumes and dairy. Try to eliminate empty calories (i.e. soda pop, junk food, etc.) and slowly make substitutions in your diet for something with a lower glycemic index.
In short...the only way to affect permanent healthy weight loss is through permanent healthy lifestyle change. I'm not a certified expert, but I have lost over 70 pounds and kept them off -- four years ago I was edging on morbidly obese, now I run marathons despite a sciatic nerve injury.