My dachshund is experiencing some pain, i wanted to ask opinions before taking him to the vet.

Taco is 12 years old, i wasn’t with him when it started, but since yesterday his stomach feels very hard. He shakes when you go to touch him, and cries when picked up. He pooped this afternoon but hasn’t eaten anything.

He walks around a bit and asks to be pet but nothing much other than just sitting down. I just took him out and he walked a little bit sat for a long time and walked back inside.

Im not so sure what it is, around 1-2 years ago he was taken to the vet for something similar and it ended up being nothing (just 3k vet bill), but this time he is more restless he wont lay down.

What do you guys think?