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 o lices.. But we bathe him all the time so l don't understand!! Even gromming,.. he looks perfect!

-Please HELP