first off - crate the puppy and let him rest
even though that is more exercise than is adviseable....I would be worried about his joint conformation and possible problems...
Rest him tonight and tomorrow - then get him into a vet for some x-rays to look at his hips....yes, he is young but if they are seriously poor, it will still be obvious...
Hope he just overdid it and is a wimp!
Csabre Sch1, Hexe Sch2, Bengal, Komet, Kyra, Kira & Kougar v Wolfstraum ~ - Danger Sch1 SAR - ATB~ Kougar Sch3, Kyra Sch3, Cito Sch2, Alice Sch1, Kelsey CD, Ret ~ Basha Sch3, Fenja Sch3