My 9-week-old puppy yelps in pain with no visible injury. What's wrong?

Hello and welcome to Petco Pet Education Center, formerly Petcoach. I am sorry that Beau isn't feeling well. Crying intermittently with no external injuries can be caused by a number of factors. If he is reluctant to walk or limping, then either a soft tissue injury in a joint/fracture/ or torn ligament is possible, however this you would expect to see some limping. Puppies can also get 'growing pains' and conditions of their joints, which affect all of their joints equally, so they are just reluctant to move. This can be incredibly painful and requires strong pain medication. The other common cause of crying out can be gastric pain. This can be caused by Beau getting into something he shouldn't have (bones, garbage, raw food, socks, underwear, etc) and his abdomen being very sorry. Usually with this you will see a reluctance to eat, possibly vomiting/diarrhea, and sometimes pain when you push on his abdomen. If this is the case I strongly suggest to stop the Deramaxx (hard on the gut, especially so young), and to have him re-checked by your vet and x-rays performed. An ultrasound may also be needed to make sure he doesn't have a peritonitis (infection in his abdominal cavity). He could also have a gastritis from worms, so making sure he is up to date on his worming is needed. A fever can also cause animals to feel unwell, so a full physical exam including his temperature is important. I would strongly suggest a re-visit with your vet, and they will likely need to do more tests, like an x-ray as mentioned, or if no answer is found there, or if Beau has a fever some bloodwork may be needed. Best of luck with Beau. I hope he feels better soon.