Flu or something else?

My wife's been dealing with nausea, diarrhea, and dizziness whenever she moves too fast for three days now. She's got a killer headache, too. Usually, Advil does the trick, but lately, even Tylenol or Aleve aren't helping much.
She seemed a bit better yesterday, so we didn't head to the clinic, but now she says light is bothering her.
Any idea what this could be?

So, how bad is this headache? My first thought is definitely a migraine.

My eyes hurt. Sometimes it’s sharp, sometimes more of a dull ache. Just feeling generally run down, too. No fever, though.

Dizziness, intense headaches, and light sensitivity can be pretty specific red flags for meningitis...
That doesn't mean you definitely have it, but it does mean you really ought to see a doctor immediately.

The silver lining is that if things start looking up after three days... even if it is meningitis, there's a much higher probability it's just viral, which rarely leads to serious complications compared to the bacterial kind.

Honestly, the first thing that jumps to mind for me is migraines. All those symptoms you mentioned are pretty much textbook for them. Of course, you really ought to go see a doctor just to rule out anything more serious... though even a migraine is definitely nothing to mess around with.

Thanks for all the input, everyone. She's struggling quite a bit in the mornings and late at night, though she seems more or less fine during the day, so she's refusing to see a doctor. I guess I'll have to talk her into it.
She hasn't dealt with migraines before.