I'm exceedingly late to the party here, but now you've probably all gone I have finally found my people!
What's being described is exactly what I have had for the last 5 weeks. Started day before Xmas eve with chills and temp, aches and pains, fatigue and gastric issues - nausea, diarrhea, bubbly tummy, no appetite. Dr said it was virus, another said possibly flu (although no chest / cough / cold - only sinus pain and headaches) but he said that he'd seen quite a few similar cases of flu without the typical 'cough cold' symptoms but gastric issues and diarrhea instead 'within the community'.
Anyway - 5 weeks later all the fever, aches etc have gone and all the gastric issues remain. I've only eaten white food for five weeks in small amounts - white bread, crackers, cake, crisps, cheese, pasta, bit of fish and chicken, bananas - no fibre, no fruit and veg - and I usually eat a pretty healthy diet so it does have me worried after all this time. I'm taking vitamin supplements now and kefir as well. But it has been awful and I'm so fed up with it. I've lost loads of weight.
Thought I was doing better this week then on Wednesday the nausea hit me like a train again. Again much worse in the morning and better later on in the day. Going back to the docs on Thursday, so fed up of it - and yes, the nausea makes me feel anxious too. I[ve just pushed two Tuc biscuits down and my tummy is making loud protesting noises. Also I really can't stomach coffee at the moment, yet I'm usually a coffee fiend.
I had something similar to this that lasted for a couple of months about 3 years ago - at the time they did tests for Inflammatory Bowel Disease but nothing was found - I do however still have high inflammation markers in my blood tests (some taken just before Xmas) so it does make me wonder.
Anyway - pleased to have found a bit of reassurance from this thread that I'm not alone!