I guess "ditto" to all the above.

I doubt it's a Red Flag /ER Visit tonight situation;
but YOU won't feel good till you get him checked out!

Start with the Shelter:
Worming date, medication, and did they see anything "come out"?
What did They feed him?
What were his poopies like during his stay?

Note: "Bag & SAVE" some of his "stuff" tonight or in the morning
so the White Coat has a sample to test.
DOUBLE Bag and store in the fridge (might 'forget' to tell Terry
WHERE you're storing "it").

As for the "free check" on the 15th or Your TRUSTED Vet sooner?
I'll pay for YOUR Vet if that helps.

I do think it may be a case of Nerbz with his Change of
Residence amd/or food change...
but "let's" get him checked ASAP