Oh how to lose the "baby" fat?

Before I had Sarah I was a relatively trim person and always had been. Now I wasn't a size zero and could never be, but I was an 8-10. I was 126 pounds when I married, but Grad school put on about 12 pounds and I'd gained 2 more by the time Sarah was born. I'm now 45 pounds heavier than that. I hate the weight but I'm not sure how to lose it. Exercise is difficult because I have this straight neck and constant pain in my upper shoulders and neck. But, I'm going to start walking - that's the least I can do. I like food but I'm already eating less. I need to work on my choices some. Most of all though, I think it was just the double whammy of having a child and turning 30 the very next day! By the time Sarah is 5 - this year on September 7th - exactly 3 months away - I'd like to have lost the weight. 45 pounds in three months? Let's see...