Thanks. I thought "wyt" would be better as the sentence is a question but does it not work that way?
No. It is to do with a particle which can follow question words such pryd, pam, etc in the more formal language. Pryd wyt...? is fine in the colloquial register (and I have amended my earlier comment to reflect that).
Maybe I'm staring to understand.. So it's not "wyt" because it's not asking IF you drink tea but just WHEN..? (sorry if all all these questions are annoying, I absolutely love learning the welsh language, it's my favourite one on here, so I want to make sure I get my head around everything!)
That is exactly right. It is an invisible 'if/whether' particle which causes mutations at the start of questions and the use of wyt rather than rwyt in questions.
In the formal registers of the language these particles are explicit and useful, but then the system of using verbs is rather different in several ways.