Why do I wake up with sore/tender muscles after sleeping in for an hour longer than usual?
I don't feel this way after sleeping my regular time
I don't really exercise if it helps
You're muscles need movement or they will feel sore.
Get out and do something.
Go an hour long walk everyday and do some daily calisthenics. You'll feel better.
Could quite possibly just be dehydration. Especially since it is summer.