Help something wrong with my lovebird?

i have 2 lovebirds since 1 year but now for the past 2 months one of my lovebird,s beak has changed ir has become rough and it looks like it has crack on it and his legs also looks like that but he can hope walk and fly without any trouble but since last one week it is tugging its beak in its feathers he turns to the backside and tugs its beak into the backside frather behind its head when it is sitting on the perch or in the night time but it eats normally and chirps everything looks normal then what might be the problem is it getting old the other lovebird has no problem