My 11 month old bitch finished her season about 3 weeks ago now, she was a bit out of sorts during her season which i am informed is quite normal. (its been a long time since my bitches had seasons!) After she finished she went back to normal training wise, although i've noticed she is a bit more clingy, she sleeps on laps now which she would never sit still enough to do before and doesn't seem to have the exercise tolerance she used to. She was very active before her season, always on the go wanting to play, but i notice last night that she was the first one to flop after 20 mins play with her sister, her sister was still going strong but molly was so tired she jsut laid on me and didn't want to get up when i said it was time to go home!
Could it be a phantom pregnancy causing this or is it too early? She's bright in between times so i'm sure she's not ill. Will she get back to normal in time?

If it's a phantom and she really believes that she's carrying pups, she is going to go the whole 9 weeks.  And then she will get a little worse while she is caring for her imaginary puppies.