I have 3 rats, one that I rescued and two that I bought. I've tried everything to get them to play together but the rescued one just attacks the other two all the time.

Anyway, he has been hurting himself somehow, maybe scratching too hard, i keep finding scabs and blood on him. I can't find any evidence of fleas or anything so all I can think is that he does it because he's lonely but he just will not play with other rats.

If he keeps doing this he's going to get an infection or something and it scares me, he's my favourite rat and the one that I spend most of my time with (my girlfriend plays with the other two)

Can anybody offer some advice? I thought maybe he would be more friendly towards a female rat, so I've been on the lookout for a fixed female, but I don't want yet another cage to clean so I'm afraid to try and find him a companion.

Edit: I treated all 3 of them with some ivermectin that my girlfriend picked up from the pet shop, what horrible stuff, I hope it doesn't make them ill but I followed the dosage and it was intended for rats...