I have a 12 week old kitten who has been with me 2 weeks. The first two weeks she was very playful and energetic and sleeping several hours then having a play then sleeping again. However the last two days she is no longer like this, she is eating well and pooing plenty but she just wants to lay all the time for the last 24 hours all she has done is sleep then go for some food then sleep. She's also stopped cleaning herself and no longer likes to be stroked which she loved a few days ago. Is this normal ?

My adult cats sleep at least 16 hours a day, so your kitten probably is exhausted from all that play. Let her sleep.

Might be iron deficiency, check if her gums are white, if so she could use some kittens milk, you should be able to find it in a can anywhere that sells pet supplies

If her gums are pink she's just a lazy kitty