If Tamiflu worked does that mean he had the flu?

[Anonymous]

DD is under 6 months and was sick last week. Doctors prescribed Tamiflu because he was sick and it did the trick -- he's feeling much better and is improved. If that's the case, does that mean he had the flu? I'm asking because now I'm under the weather and don't know what I have and I also wonder whether he should get the flu shot in a few weeks when he goes in for his 6 week appointment.