Don't go into "worried mom" mode yet. It could be HD, and the symptoms sound like it. Normal, healthy puppies are not stiff when they get up after laying down.
Have him x-rayed (they are not dangerous to him)...and it's better to know what is going on earlier than later. I have to tell you when symptoms of HD show up in such a young pup this early....it's usually not good.
What are you feeding? How much does he weigh? Slowing down his growth and having him gain weight slowly really helps....because the ligaments, joints and bones have a chance to catch up with the body.
If a dog has severe HD, they should not be jumping in and out of high vehicles. We bought a mini van so that the floor was lower and easier for our Bruno that suffered from HD could get in and out.
Even if puppy has been running on slippery floors it has not created HD....it may help to have the symptoms show up earlier, same as diet,etc....but slippery floors does not cause HD. If you got your puppy from a BYB, it could very well be the reason for HD.
Let us know what happens.
Gina