It is difficult to be a middle child. I am one. So speaking from experience You have your Older sibling who attempts to be wise and in charge.....Then you have your littlest child that is always to young to understand and the other children should know better not to fight and argue or whatever.
Your middle child I think needs security while your other 2 children have a role as being the First child and the last child...HE does not have a role he is more in between the 2.
I have heard once that middle children typically end up having the fewest pictures in the family photo albums and I thik it is true in most cases. Not that the parents are neglectful it just happends that way when you are so happy there is your first child and your taking pictures like mad and along comes your second and while your taking pictures of him here comes your last child and they seem to take up so much more of the film because they are your LAST child....
Anyway I am not an expert but i would say that he could be more sensative in the fact that he does not know what his role is in the family I think he needs moments when it is just you and him in the picture I think all children need those moments. If his dad is in the picture at all i and a good influence i would suggest having him spend timw tihe his dad tell him that your son needs to feel sspecial and important..
He needs security in knowing that you think he is special and love him just as much as the other 2. Even if you are a parent that does not show farorites every child i think needs to feel like they are special for some reason...Look for his talents and gifts and build on that...
if he is the only boy maybe let him feel he is the man of the house when dadddy is away... That can help him form his identity...
I hope this helps.