All hamsters store food in their beds, its a natural instinct for them. They will take food out of their food bowl, stuff it in their pouches and keep it in their beds for when they're hungury. Hamsters don't eat very much, it sounds like you're giving him the right amount of food
If you're really concerned try giving him some fresh veg/fruit and see if he eats it. Are his poos normal?
And my hamster does exactly the same as yours, he moved all his bedding from his igloo and built a nest in the corner of his cage. When I put his igloo in that corner he pushed the igloo out of the way and built his own nest. Some hamsters prefer to have an open nest
I like watching him all snuggled up asleep