Can i bathe my chihuahua weekly?

I have a chihuahua named socks, and he is VERY energetic. He loves to jump around and play outside. So by the end of the day he smells.. not so good. He is pretty big for a chihuahua the dog breeder said occasionally there is one big one in the litter. And he is around 14 maby 15 weeks old. We have not taken him to the vet yet. We will soon. I just wanted to make sure if it was ok to bathe him once a week. and should i use an oatmeal bath?i have noticed after baths he scratches. I have checked him for fleas and found nothing. And i hear sometimes that chihuahuas get itchy skin... Is this true?