You do sound done in. could you be going through a bout of depression and are mistaking i for no energy. Maybe a check up would be the first thing to look into (for yourself). I agree with everyone, Dobes are high energy dogs, but they also need an alpha to look up to. Taking walks might just not be enough for the pup. Is there an enclosed area somewhere where you could bring her to play ball and let her run? an unused school field, or rink? You also need some hlp learning how to cope and handle the dog....have you looked into training classes? You will learn a lot and so will your dog, plus they're lots of fun. Anywhere that you could take her swimming and throw a ball in for her to retreive?
It would be such a shame to have to rehome the dog. Dobes are very sensitive and are mostly one owner dogs. If you just can't find feelings for this dog then you would have no choice but to find her a home with someone who will give her what she craves most....love.