Is this normal for chick behaviour? Slow chick

[Egg_cited]

This is my 3-4 week old cockeral. He hatched out as a lonely chick so I bought him some friends. That are 2-5 days old. After I bought them he become much more slower and not as active as he used to be. He still drinks and eats but has these random moments when he's just slow. Am I overreacting? Please help

 

[nuthatched]

Where did you get the new chicks?

 

[BlindLemonChicken]

He looks small for his age