Ok, this is one I haven't seen before. Was wondering if anyone had any clue as to what could be the problem here ...
My 5yo healthy as a horse Beagle bitch was in the yard today, she was the only dog out & I was right outside with her. I know for certain she was not injured in any way. When I let her inside, I notice that while walking up the stairs, she is holding her tail in an odd position. It's straight down - she will not hold it up for anything - and also about halfway down the tail she is holding it curved sideways

When I hold up her tail she looks very uncomfortable and keeps the tail stiff as I try to manually straighten it. Not crying or whining but it's obvious she's not happy about it.
I've had her on 250mg of amoxicillin for 3 days as prevention, because her pups (7 weeks) came down with a bit of a stomach bug, which I did not want her to catch. So momma & pups were on antibiotics. I don't know if that has any relation to this new problem w/ the tail, but thought it may be worth mentioning. Also, I've had the feeling this dog was not herself the past few weeks. She escaped from the yard about 2 weeks ago and deliberately walked off in the opposite direction when I called her. Yeah, Beagle. However,
not normal Heidi behavior. I had to go seraching for her & found her across the street ... at which time she did come over to me.
I am thinking she may be in pain, the first thing that came to mind was maybe spinal problems. But have had a few dogs w/ back probs and they have not done this with the tail. They usually just have a limp that worsens. Any ideas?