From all I've read, and my little girl going through the exact same thing, at that age, what you describe is typical behaviour. They start to have an idea of "object permanence" from about 7 or 8 months old, in other words, for the first time he realizes that you are separate from him and can actually leave (before that it is just, out of sight, out of mind). So he starts being afraid of you leaving. He might also have a little bit more trouble with waking up at night and crying for you.
It is a developmental stage and means he is on track. It does get better in a few month's time, promise!
There is a great book (and app) that describe these stages perfectly. It is called "the wonder weeks" (
). I have a kindle so I got mine from Amazon (which is cheaper than the hard copy). It describes all of these fussy periods, the reason behind it and also gives some suggestions and solutions.
It boils down to the fact that, in the same way a little one's body goes through growth spurts, his or her brain also does the same and each one opens up a whole new world for them. They will then get fussy because everything is experienced differently.
There's a great group on Facebook also for this - lots of women going through the same.