Hi Mav I'm UK to and totally agree this weather is seriously rubbish, its never affected me as much before but really feel the winter blues. 15 days is brilliant. I'm recently sober to and after the initial high wore off I was left with a bit of doubt, fear and panic. It was also quite scary actually having to deal with coping with stuff that were triggers without alcohol involved. I'm having a crappy day today fantasising of sunny holidays just generally that kinda can't be arsed day. But I kinda go with it now everyone has rubbish days and tomorrow is usually better. I had much worse days when I was drinking and hungover.
Generally I feel amazing physically and mentally much better since stopping so stick with it. If you are concerned talk to your doctor. 15 days is a really good achievement.