Thanks for your patience :)
When I see dogs, especially dachshunds!) who just "aren't doing right" combined with tense bellies and yelping when being touched after heavy exercise, I'm strongly suspicious of back pain. dachshunds are the poster children for intervertebral disc disease, which can be a very painful disease. Its symptoms can range from mild pain all the way up to complete paralysis in the back end. Thankfully, the paralysis isn't terribly common, although it does happen. When their back hurts, they will tense up their bellies in order to keep their back still - they are guarding their back. Many owners describe to me that their pet yelped when they tried to lift them from under the belly - the reason their pet cried is because they it hurt to arch their back. In the vast majority of cases, eating, drinking, and eliminating normally means they're stable enough to wait until the morning for a vet. I'd call your vet tomorrow and discuss the potential for back pain - as he sounds like a pretty classic presentation to me. I usually treat these guys with rest, anti-inflammatories, and pain medications. I sometimes even start with an injectable opioid pain medication while they're in the hospital if they've been quite uncomfortable. They usually do recover quite well, but the problem can be recurrent or in uncommon cases it can progress to weakness or paralysis in the back end, which would then be an emergency. I usually recommend keeping them exercise restricted - no activity other than out to potty, no stairs, no jumping, etc.
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