Head hurts/heavy days after what appeared to be flu, why?

[ChazzyAB]

About a week ago (Monday, Dec 5th) around 9pm, I began vomiting and having diarrhea. At first I thought it was some kind of food poisoning, as it came on a bit after I had ate. It progressively got worse and worse. 7 hours later, I was still vomiting and using the restroom profusely. I was in very much pain. I decided to take this situation to the ER.

Couple hours, an IV and some meds later, I was sent home with the end result being gastroenteritis. No longer vomiting for the next few days but still diarrhea, the "sick" feeling in my head was still present. I proceeded to wait a bit longer for all to subside.

About 4 days ago now, still no vomiting, no more diarrhea but rather one full day of constipation — proper diet for when having flu-like symptoms, slowly eating more, proper hydration, etc., all taken care of — but the head feeling...still present.

Next day, all flu-like symptoms are gone but the head feeling still there, As it is today. It feels heavy, tingling, headache-like at times, tired (always. As if I haven't slept, even when I have). I feel slow, foggy, sluggish...sometimes feels as if it's harder to process things. It does not lesser, it does not go away, it's there from sunrise to sunset.

It is now 3:30pm on the 11th of Dec and I feel no change. I do not feel sick of any kind. Just this massive feeling in my head that I cannot figure out. It's extremely bothersome. It ruins every day. It's making me anxious. Even my vision...just the way I look at things seems..off, different.

If anyone can please help me...