Well mystery solved why I'm struggling so much.
Turns out my thyroid is naffed. I've been borderline hypothyroid in the past, more so when I've been unwell and my absorption has been poor. I was so ill throughout my pregnancy, then lost 2 litres of blood having LO (low iron levels can heavily affect thyroid function) so it's not at all surprising.
It explains why I've been fighting a battle with myself to do any exercise and why my weight is not coming off like it should and why I can be so constipated despite drinking litres and litres of water every day and eating nothing but fruit, veg and nuts.
Cracking out the thyroid boosting foods now, but I think it's going to take some time so my weight loss is going to be exceptionally slow.