Worried mom - before i go running to the vet!

So i'm wondering if i need to be concerned or not.
Last night snoopy seemed pretty drowsy and after she woke up from a nap i went to go roll her over and scratch her tummy and she kept letting out little yelps...
so i picked her up... yelp...hm.
so i rolled her on her back and felt all over to see what was hurting... no yelp...
pick her up... yelp...
??? and since then she has been VERY drowsy...slept allll night without a peep and didn't even wanna go outside to pee this morning - just went to her crate and back to sleep...
sometimes she yelps on her own... sometimes when i touch her.
and she has a very abnormally low energy level (not that i'm really complaining but..ya know)..
does anyone have any ideas????? :S
thanks