Oedema :: Both Feet, Ankles And Calves

Several days ago, I developed Edema (or Oedema) overnight in both my feet, ankles and calves up to my knees. This is my third bout of edema. The first was last year but only in my right foot and the second time was a couple of months ago, again in both feet and ankles but was very mild.

Two days later, the swelling became so severe, both my feet looked bruised and turned a funny red colour. The pain became that powerful, I couldn't walk whatsoever.

Im in UK so I rang 111 NHS helpline who sent out an ambulance. The paramedics arrived and were shocked as they had never seen edema so severe before. This was a Saturday and my GP closed so they arranged an appointment with an out of hours GP at my local hospital  in the next hour. 

He had no idea what the cause was and was that worried, he sent me to another hospital 30 miles away to see a specialist. I arrived and was admitted in straight away for tests and observation.

They took blood and urine tests, a chest x ray, a heart reading straight away. But they couldn't link a diagnosis with the edema. They flooded me with antibiotics assuming that it was an infection.

I was discharged the day after as the redness and pain levels seemed to have gone down a little after the antibiotics and i will be returning soon for an ECG and other scans. I left with walking sticks so that I could walk around easier .

Now today its been almost a week. I still need the walking sticks to walk, the swellings is still huge, the pitting is still evident but i do think the antibiotics is helping some.

But I really wish I could know what this is as its very worrying. The docs couldn't see a problem with my heart, liver or kidneys. I have also been tested for DVT and gout. My blood sugar is fine. The only possible resolution is that it cold have some link with the hot weather, but that wasn't confirmed.

Has anyone else had severe painful edema in both legs and the doctors  couldn't find a diagnosis?

My current medications  I take regularly are: Mirtazapine 45 mg and Hydroxyzine 25mg. 

Can anyone advice or share  their experiences? Is there anything I can do to help minimise the risk of this happening again? If this is heat related, I'm going to have a hell time every time it gets hot. But surely 'hot weather' cant just be the only explanation there is why I have major swelling in both my legs and feet.