I wish I could tell you something to help - but it could be the medication....hopefully it's working and she's ok but that can cause a change in behaviour - but I would tell the vet this...you know her the best out of everyone and if you think something is a bit off - then maybe it is ?
I did notice a change in both mine getting calmer after a year old - but they wake up EARLY and always ready to play. Actually they go to bed ready to play too.
Chanel is 4 and can play with her toys round the clock ....while Cheri is a little more of a napper.....Nobella may be right - they do take cues from who they hang with LOL