OK. Look maybe I was harsh.
It sounds like he is being 'cute' and learning words by rote, like when they first bring words home eg, cat, mat, rat. If they are always shown in that order they don't necessarily see the word, they just remember it.
First of all, don't panic ! Reading comes easy to some, not to others. Make it fun, and no pressure. It will come eventually.
As others have suggested, you can 'read' all the time, food, shops, sign posts, there's loads. I used to make little 'word cards' and write certain words and then put them all over the house, it becomes almost like a subliminal learning.
Don't feel angry with him, it may just be taking him longer...you can also buy word packs to help with reading, go easy on one another and start off just with 2 and 3 letter words, and progress as you need to.
HTH 