We have three guinea pigs, all sisters, all have been with us for around 12 weeks. The youngest always followed her big sisters about, which we thought was normal as human kids do that too! Just this past week though, she's been following the middle one around, but sitting her head on the other's back/bum. Is this aggressive or is something wrong? I keep trying to separate them as it's annoying the other guinea pig and I don't want then to fight. Any ideas are greatly appreciated. (Our first time having guinea pigs).