Hiya LMS, first of all well done for sticking to it since November! I really don't know for sure, the only thing that came to mind was what is your diet like, are you restricting any food groups? I know when I was low carbing I would get terrible leg cramps due to low potassium, I used to take a potassium supplement or if you can have them you can eat bananas for a quick potassium fix, they give you a good energy burst as well. Even if you have a balanced diet, if you are drinking huge amounts of water (say more than 3 litres) this can wash nutrients through your system before you have time to absorb them, so it could still be a mineral or vitamin deficiency.
But please these are only thoughts and I don't know for sure, if the pain is that bad I would see your doctor! Probably nothing serious but it's best to see the expert. Hope you get to the bottom of it soon! x