This all sounds normal. I havn't had an Amazon, but they are kind of well-known for this sort of thing. You will need to work on training him and you don't want to react to the bites in a way that reinforces them. In order to do this, you will need to figure out why he is biting. If it is
to get attention (yelling, eye contact, the presence of a particular person etc),
avoid something/escape (not wanting to step up), to
get something/tangibles(like a favorite toy) or for
sensory reasons (hunger, lack of sleep, fear, developmental etc).
Do an ABC chart to track what happens before and after biting (antecedent = what happens right before, and consequence= what happens right after (consequence is not bad- it just literally means what happened right after---did you laugh, cry, yell, run away, drop the bird, give it a toy, sing a song, turn away, pet its head etc etc).
Search for ABC chart on the forums... (here is one link that includes my response related to ABC charts-
http://www.parrotforums.com/conures/77273-there-something-wrong-my-conure.html --2nd reply to OP near bottom) I have talked a lot about this. Ultimately, you will want to show him that his needs can be met without biting (through more acceptable replacement behaviors). Also, ALL birds change from the time they are babies. Just like baby humans, really young baby birds are sweet. Then, similarly to humans, birds also have a sort of "terrible twos" phase, followed by puberty (and all of these include biting).
There are mixed opinions on how to respond to biting and I do think the fact that your bird is a baby will make a difference. If it is truly due to the fact that the bird doesn't know, then say the same thing each time and make the same face. If it is innocent biting, then your bird will learn that biting makes you unhappy if you follow the same routine. Never shout or punish though, as birds like loud noises and they also do no understand physical punishment.
In adult/older birds, I believe that saying "no" etc can sometimes make the problem worse, but it does depend on the bird and what they are after when biting.