I used to have the exact same problem of not wanting to eat/drink, but didn't get a headache, I wanted to throw up right after brushing until I found
out I was allergic to Flouride, and changed to a non-flouride brand. I don't remember if it gave me headaches unfortunately, its been almost 30
years since I stopped using flouride toothpaste. Damn shame that strawberry kid's one had flouride in I LOVED that stuff.
Oh, and I'm also slightly allergic to propylene glycol, which is used in some pastes as a thickener, so it might be that, check your label see
what's in it.
Try a non-flouride brand, maybe that'll help? Worth a shot, and its not like you'd waste it. They do unpleasant flavours in some health shops
though, I got aniseed and teatree the other day, damn that's a disgusting mix.