Your dog might be going through their spring shed. I have three dogs that are going through the same thing right now, because it is getting warmer outside. They are loosing their winter coat and growing in their summer coat. All dogs shed more in the spring and sometimes even in the late fall. All dog, domestic and wild shed a lot in the spring. All you can do is brush him once a day. You can brush them with a special comb that works wonders, here is a picture of it. It pulls out any loose hair and I use it on all my long and short coat dogs.
I find I get a large amount of hair when using it, the dogs shed less and go though their shed faster too. You also can feed your dog ground flax seed mixed into their food and you can give them one cod liver pill a day, it will give them more oil in their coat and they will not shed as much.
Have you read my web site page http://joneschihuahuas.com/?page_id=831 it is about why dogs shed.