Well I'm not good at guessing genders at all. I posted pictures of my chicken that I thought was a rooster and people are saying he looks like a hen. So I really don't know what yours is. Kind of looks like a roo. Maybe he's a late bloomer. Sometimes they don't crow until their 6 months old.
Are they aggressive to the point you think he's being hurt? The actual mounting shouldn't really bother him (I think). Is he lethargic? I would worry about a chicken laying around so much.