Do I have carbon monoxide poisoning

Basically I burned a piece of tissue paper on a flame (about the size of my hand) twice in my room next to my window (which was open).

Since then I've felt a very slight headache. Is it possible I have carbon monoxide poisoning?

Not at all. It takes a lot more than burning some paper to create enough CO to cause a problem.

You may have a headache from the smoke, but there is no risk of CO poisoning.

Take some over the counter headache medicine.

I doubt it. You would get more carbon monoxide from a cigarette than burning tissue paper by a window.