What's up with my cat??

l have a 1 yr. old male cat and he lives in our house since he was born! He was a few times outside but only on a shortleash, my sister is too afraid of leting him out because we live close to road-way..
So l don't know why does he scratches himself always after he wakes up from a sleep! He's doing that for about 3 minutes.. It really annoys him. Mom thinks that is ridiculous to call the vet for that
He loves to go on an attic of house so maybe it's from the dust of lices.. But we bathe him all the time so l don't understand!! Even gromming,.. he looks perfect!

-Please HELP