Can You Over Exercise A Dog?

Yes it is possible to over exercise a dog. Dogs who are devoted to their owners may not complain even if they are tired. In an intense urge to please the owner, the dog may continue to exercise till it collapses. This should be avoided under all circumstances.
While exercise is extremely important for a dog as it is for humans, the type of exercise varies based on age, breed, and health conditions of the dog. A young pup may have lots of energy while a old or over weight dog will not be the same. Hence running may be suitable for a certain dog but walking may be best for the other.
Signs of fatigue should be looked for. The dog can pant excessively, it may give a blank stare, the lips and the face may loose color, or it may even have bleeding paws. If you see any of these signs you should stop immediately.
Moreover, do make sure you give enough water to your dog such that it does not dehydrate.

When your dog is so tired it doesnt even want to stand up then you know he is over exercised

Luvsdog,

Your query reflects that puppy is too young. You can start exercising him when at the age of 5 months. They love to play and exercise on the running guard. Please have a look at the link below.

http://www.runningguard.com/

OR

http://www.dogchannel.com/

Let me know if the given links are fine.

Thanks

The amount of exercise a puppy needs depends on the individual puppy, the size and breed of puppy.  Extended periods of activity can place stress on the musculo-skeletal system that is developing.  Small, frequent bouts of activity are the best for puppies--they usually like to play hard then sleep hard. 
Five miles does sound long for most puppies.  Also if you have the puppy off leash most dogs actually walk/run farther because they rush ahead then run back to you multiple times.  I do not recommend long hikes or runs with dogs until they are 9-12 months depending upon the dog.  High intensity and high impact exercise can affect development--just like human gymnasts.
Puppies are very sensitive to hypoglycemia and dehydration so bringing along adequate food and water is very important.
There are some developmental diseases that can affect puppies especially large or giant breed dogs--if the lameness persists please have  the pup examined by a veterinarian to assess the joints-especially elbows, hips, and shoulders-as well as the long bones.

No the more exercise the better this just means that the puppy is in good health.

Best to take them for short walks at a slow pace until they're around 9-12 months (depending on the breed) to avoid irreversible developmental problems. Puppies should be allowed lots of 'free running' off-lead play time. A 'short walk' could mean 15 mins, but I think your best bet is to stop when the puppy begins to tire.

I'm going to guess its rare but yeah. Does yours have any symptoms?

Yes, you can, you can cause some pretty bad pain for the pup that way too. Not good to do to them. Hope this helps.

Yes you can. To much exercise can hurt your dog in the long run. Excessive amounts of heat from being outside can make things worse.