Do more side-quests!
First go to the Death Mountain again. As other people said it is not inside the mountain but a bit more on the left side and you need bombs to get in there. Also go to the "dead end" at Hyrule Castle, you will also need bombs.
Then try to walk around Hyrule Town and play some of the mini games at the market place, you will get some nice rewards for it.
I guess you also missed some additional items in the lost woods
How many heart pieces have you collected so far?
You need to stop using that guide, really It just stops you from experiencing more side-quests. Talk to every person in the game and explore Hyrule field.
Only then you'll see why this game is so great