[Life's a beach]

I have a 9 month old rainbow lorikeet. He lives in the house and is in excellent health.
However, his feathers on his body are starting to look straggly and tatty.
His head, neck, wing and tail feathers have recently fallen out and been replaced by beautiful intact feathers, but his body ones are quite tatty.
I have looked carefully at him and he doesn't appear to have any lice or mites.
He's certainly not lonley as he is constantly on my head/shoulder or on another family member. But he is alone as in "not in a cage with other birds."

I am home all day and he has 24/7 stimulation.
He even showers with me - he is a very clean bird and grooms and bathes constantly.

Is it simple moulting? Does he need vitamins? Or more natural sunlight?

He flies perfectly well and doesn't appear to be in distress or excessively grooming and he appears very happy and playful.

Any advice?

Thanks.