I hope you the best of luck. It sounds like your goals and time frame are alot like mine, except I actually had a lot more weight to lose than you did. I hope to reach my goal weight of 115-120 lbs by December as well. I have about 40 lbs to go, having lost nearly 40 already. I have been losing about 10lbs or so a month--sometimes more, sometimes less. I am quite consistent in what I do, and I think the fluctuations in weight loss have to do with fluid shifts. One week, for example, we got carry out from a Chinese restaurant. I was careful in the amount I ate, but, while I didn't gain any weight, I didn't lose anything for two weeks. Then, over the next two weeks, I lost an average of 4 lbs a week. Now, Chinese restaurants are on my list of where not to eat for at least the next several months. Generally speaking, I find that even if calorie counts are ok at restaurants, they use more salt in preparation that I would at home, so, I always have some fluid gain for a day or so if we eat out.
I also had a stressful time in my life when I gained most of the weight I have to lose. For most of my adult life, I have weighed between 110-120 lbs. After my son was born, I went through a very stressful time, primarily due to work related issues. I am a physician, and during much of my son's early childhood, we were short doctors in our practice, so, the remaining doctors had to work longer and harder to compensate. Between having a new baby and having to work harder than optimal, I was so exhausted I could not bring myself to exercise, and unfortunately, ate too many high calorie "comfort foods". I knew I was gaining weight, but had no idea how much. It was a real shock when we applied for life insurance back in 2001, and I weighed 191 lbs. Fortunately, at the time, my blood pressure was ok, as was my BS. Several times since then, I have tried to lose some weight, but haven't really lost much more than 5-10 lbs. Since then, I have developed high blood pressure and prediabetes. (Losing 10 lbs wasn't enough this time). That is my motivation for getting back to a healthy, normal weight. For me, it is a nice side benefit that I also look much better, even now. I know that from now on, I will need to be vigilant against gaining weight, because I surely don't want to have diabetes.
Anyway, good luck to you.