Why am I no longer able to lose weight?

I have been a fitness enthusiast for nearly 20 years, even appearing in two fitness infomercials, but after going through a divorce in 2003 and subsequent stressful life changes, I quit working out and gradually gained quite a bit of weight.

In March 2011, I decided to rectify the situation. I reduced my caloric intake, endeavored to eat healthy foods, began exercising again and took up running (which I love). Within a short time I dropped 33 pounds and all was well. I was continuing to lose weight and was only 10 pounds from my goal weight when another upheaval occurred. In January, 2012, I took a new job which I thought was a dream job. Instead it was a nightmare of epic proportions and was stressful beyond anything I ever had experienced, including my divorce. I continued working out, but it became sporadic and my eating definitely suffered. In June, 2012, I escaped to my current job but by then I had regained 10–14 pounds (it fluctuates).

I have been at my new job for six months and become accustomed to it (it’s a good job and pretty stress-free). I went back on my healthy eating/regular exercise plan three months ago, but to my surprise I have been completely unable to lose any weight whatsoever. I have tried cutting calories further without success. I have tried increasing calories, since someone suggested I might not be eating enough. No dice. I’ve lowered my carbs, cut down on sugar, etc. Nothing. I am mystified and although I have not lost my motivation, I am frustrated. I would be happy just to re-lose the 10 pounds I have gained back whether or not I succeed in losing any more than that and ever reach my original goal weight. I’d just like my clothes to fit and some of them now don’t.

The facts: I am 49 years old, 5’9 inches tall and currently weigh 153 to 157, depending on the day. I exercise 6 days a week and take 1 rest day generally, but will take 1 extra rest day if my body tells me to. I run 3 miles at 5.0 mph at least 3 or 4 days a week and on the alternate days I do a variety of workouts combining things such as lifting moderate weights and/or using body weight resistance, stretching and barre/Pilates and kickboxing. For the record, my hormone levels indicate I am perimenopausal, but I have absolutely no symptoms or side effects and I have been in perimenopause for years. It didn’t affect my losing weight before, so I don’t think that’s a factor now either.

I am interested in constructive suggestions about what might be causing this plateau and how to break through it or information and encouragement from others who might have experienced the same thing and succeeded in getting through it.