For a couple of weeks now I've been experiencing some really confusing symptoms. It started when I had to go walking around outside when it was about 30 F. When I got back inside and sat down I felt a little nauseous and my head felt unusually warm, but nothing too bad. Went to bed.

Woke up in the morning extremely nauseous, over the next five days had very watery diarrhea and occasional vomiting. Kept belching up stomach acid.

Tried taking antacids and such to no avail, but symptoms almost completely stopped after I took a hot shower.

One week later after everything's been normal, I had to walk in the cold again and now my symptoms are back. Gets a little better after hot shower, but it worries me that this seems to be a persistent thing. What could be causing this?