Today we noticed that our piggy Cedric is smellier than usual. I have also been noticing that when he poos, they are darker, smellier and stuck together. When they are single ones, they are smaller than usual. He seems normal, he's eating his veggies, hay and seeds. I haven't checked him out yet to see if there's a lump near his bum, but I'm afraid it's impaction. How do I know for sure? We have recently changed his brand of seeds, maybe it's that? Also sometimes if he eats too many carrots he gets a little sick. If it's impaction, I know that you can clean your piggy's bum yourself, but mine is very squirmy, there's no way he'd lay upside down for me, and I'd be afraid I would hurt him. Should I take him to the vet? I know impaction can be very serious if left untreated. How do I know if it's getting worse? 
Thanks !
Thanks !