So, three words, homophones, where a homonym  would work perfectly well. Okay, “yeah” is  pronounced  a bit differently.

As I understand it:

• Yea = an affirmative vote. Rhymes with, but opposite to, “nay.”
• Yay = I’m really happy
• Yeah = a slacker’s “yes”

Would the use of the wrong one ever be misinterpreted? Yea… or would that be yeah? Yay.