Weight gain after good loss

Hi, I have never had a problem losing excess weight gained after having 3 children or after putting a few pounds on during the winter etc. I just had to up my exercise and watch that I cut out junk food. A few years ago, during my late 30s, I put on about 3 stone after going through a divorce and housemove and let my exercise and diet totally go to pot. After these stressful events had passed, I decided I needed to loose the weight quickly so I went on a low carb diet, eating just cereal and toast for breakfast and then low fat protein for the remainder of the day. I went to the gym 3 or 4 times a week. This worked for me and within 6 months I had dropped the excess weight and was back at my usual 9 stone (I am 5 ft 4). However, I began to feel tired and lethargic so I was advised to eat a more balanced diet and spread my carbs out throughout the day rather than just eating them at breakfast time. 18 months later and I find myself at 11 1/2 stone and I cannot shift this excess weight, no matter what I do. I don't want to go back to the low carb thing as I don't believe it was good for me. I have tried counting calories, I have cut out all alcohol, I go to the gym twice a week and walk a lot, as I work full time now and don't have the time to do anymore exercise. I have been at this weight now for about a year and I simply cannot get a single pound to fall. Its so frustrating for me since I have never struggled to succeed before this. I was wondering if I have ruined my chances of losing weight easily since I lost the previous big weight gain so quickly? I am 42 years old, is it possible that my hormones are to blame? This is beginning to take over my every day thoughts. Thank you and hope you can help.