Got a 12 week female lab puppy and have noticed the last few days she seems less active, doesn't seem to be gaining weight, and walks with a slight arch in her back. Any ideas?
She stays in a pen outside with another pup but I am thinking of putting her in kennel inside tonight so I can monitor how much she is eating and when and if she is going to the bathroom.

Could be bloated/have a blockage.

possibly constipated keep an eye on him. some kind of pain is happening A vet will know for sure.

Took her to the vet last night. They did a bunch of Xrays that didn't show anything. Kept her overnight.

$482 dollars later... she ate something that stopped her up. Enema fixed the problem but before that they did xrays, blood work and who knows what else. Lord knows I didn't need that this week.

How’s the pup doing now?

After 2 trips to the vet and $600.00 they diagnosed her with Panosteitis which basically means she is growing too fast and causes lost of bone pain in her legs. Trying to keep her from moving around too much and have changed her diet to some high dollar feed they recommended. Its like having an invalid!!!
Typically takes 3 weeks to get better and can reoccur until they are 2years so I am told.

Man hope you guys get her passed all that quickly