Cardio exercise requires glucose as its preferred fuel source so perhaps you are just not eating enough Carbs for your body to function properly with the added stress of exercise. Carbs are like the tinder that helps to ignite the fat. If you have very little carbs in your system then your body will find it very difficult to burn fat and it will rather convert your lean muscle tissue into glucose for it to use as energy. You definitely do not want your body to cannibalize your muscle tissue.
Muscle burns more calories at rest than fat does, so the more muscle your body has the more calories you can eat without putting on weight. If you want to burn fat during your workout it is important to eat enough carbohydrates to fuel your body during the workout. So it really depends on what time you usually work as to when you need to be eating more carbohydrates. If you want to eat shortly before your workout you can eat simple carbohydrates such as fruit. This won't make you feel heavy, but it will give you a supply of glucose in your blood stream very quickly. It takes about 20-30 minutes for fruit to be digested. If you prefer to eat a few hours before your workout then opt for complex carbohydrates such as oatmeal or a high fibre cereal (breakfast), a wholemeal sandwich with lean protein and salad (lunch), lean protein and vegetables including pumpkin, potato, sweetcorn or peas as your carbohydrate (dinner).
It may sound scary to someone that has been on low carbs for a long time, but this may just be the key!
Focus on calories in versus calories out. Protein generally can have quite a lot of calories because it naturally contains more fat than carbohydrate. Even if you buy the leanest meat, it will still likely have 8% fat. You may be better off working out your weight loss calorie level and then getting yourself a calorie counter to work out a balanced menu plan to help you lose weight healthily.
It may be just what your body needs to shake it out of that weight loss plateau!