"Ydw, dw i wedi mynd."
Translation:Yes, I have gone.
As I have already discovered, "wedi" implies the verb has been completed, so in this case would "mynd" mean just 'to go' ?
mynd is the verbal noun for the verb meaning "to go", yes -- you can often compare it to the English gerund, which would be "going" in this case.
- Dw i'n mynd = I am going
- Dw i wedi mynd = literally, something like "I am (dw i) after (wedi) going (mynd)" - means "I have gone".
- Dw i eisiau mynd = literally, something like "I want (a) going" - means "I want to go"
... i thought "dw i wedi bleno" means 'i am tired'. Does it actually mean something like 'i am in bed (because i am tired)'?
Think of this as an answer to something like "did you leave yet". Most organic responses are not information rich simply because, in context, you already know this sort of detail.