Thank you all for your suggestions and concern. I should have said that I have already mentioned this to 2 doctors - my GP and my Integrative Doctor, plus my naturopath. they have checked everything - kidney function fine, liver enzymes were up before I went grain free but those are now OK, blood pressure is always excellent. I had a fasting glucose test of 5.5 so I am keeping an eye on this and am sugar free as my elderly mother (82) is diabetic. I don't think they have checked my electrolyte balance though.
I am taking Dr Wilson's supplements for Adrenal Fatigue so this may be part of an electrolyte imbalance. I think maybe I don't get enough salt. I am taking magnesium and potassium, selenium etc, etc, but don't eat any processed food and would salt my food probably only 3 times a week.
I have moved to a much hotter climate than I am used to and sweat everyday much more than normal. I am sporadic with my water intake - some days I have enough, other days not so much - so could improve here.
This also happened in the last few weeks of pregnancy and every time I mention it to my doctors they really don't seem interested...
After my original post I elevated my legs and the swelling was gone over night - it is now back to a bit of fluid in my ankles which the doctors have seen many times..
So thanks all - I'm going to improve my water intake, try cutting out dairy, make sure I'm 100% grain free and up my salt intake.