How do I give my dog more energy

How old is the dog? Has he/she been to have regular vet visits to make sure there is nothing wrong health wise?

If everything checks out healthwise, how often do you or your girlfriend take him out for excersise? Your dog should be taken on at least two long brisk walks a day, and also have some play time. Dogs are travellers, and they need to be excersised. Do you have rollerblades or a bike? This helps a lot with dogs that are lazy or lethargic. (pending any health conditions, as I said)

The more excersise they get on a regular basis, the happier they will be, and in turn, the more playful and healthier. You could also ask your vet if the dog is being fed the correct food for it's breed and age, and also inquire about supplements.

Good luck! :)