Hi all, just looking for some advice here. Bit wary about posting here as some of the more hardcore forum members can be a bit intimidating so please go easy on me

Since the beginning of January I have changed my diet quite substantially. Two of my worst bad habits were cans of coke, I used to drink 4-6 cans a week and about 3 cups of coffee a day, each with a little chocolate bar - I have cut out the coke completely and have cut my coffee down to one a day with no chocolate at all.
Whilst I understand the usage of BMI to determine how healthy you are is not a perfect science, my BMI is way at the wrong end of the scale and aside from wanting to look good etc., I am worried about my health.
I exercise on a treadmill for 45 minutes 5 nights a week, this is walking at a pace slightly faster than my normal walking pace and is rehab for my leg as opposed to weight loss orientated. Due to injuries sustained in a crash I am very very limited in what physical activity I can undertake so that is about all I can do for the forseeable future. I'm under two consultants and treatment is ongoing so hopefully there will be some improvement at some point.
I understand that weight loss is more about diet though and in my case, it's probably going to be 100% about my diet because I'm not physically capable of exercising away the weight.
I have used myfitnesspal to calculate my daily calorie intake and it usually comes in at around 1,300 calories, never more than 1,400 calories.
My treadmill indicates that I burn approx. 300 calories in 45 minutes so that's 1,500 calories per week but I'm not exactly sure of the accuracy of that calculation.
I started the 5:2 "fast" diet a month ago, Tuesdays and Thursdays are my reduced calorie days and on these days I have my usual breakfast (porridge), no lunch and in the evenings I have a vegetable juice, usually spinach, kale, celery, apple and some lemon. I've been experimenting so it actually tastes quite nice and I think it's a good way of getting calories on my reduced calorie days.
Just to preface, I am allergic to eggs, red meat and have quite a few other allergies so have to be quite careful about what I eat.
I rarely drink, I can't really go out much as my injuries are quite limiting, for example, I can't stand for long periods of time so I'm not much use in a pub anyway.
I make the majority of my food from scratch in a slow cooker, cook up batches of food and freeze it.
Other than a dislike of broccoli and tomatoes, I love all vegetables.
I absolutely love fish and would eat tuna for every meal.
As I said, I changed my diet at the beginning of January and I am a bit disheartened to have been so strict with myself and not lost much weight at all.
I am just wondering if anyone has any tips for me, I would really appreciate them.