Sveva: Something MUST be wrong with your scales! I've never heard of someone gaining that much (or losing it either) in 5 days. Have you used other forms of measuring your progress--like a tape measure or clothing? It sounds like it's time to get a new set of scales.
As for your hip/leg/back pain, you are wise to take it easier with exercise when feeling pain. Fatigue and the burn from lactic acid is one thing. Pain, on the other hand, should never be ignored. If it continues, you might want to visit your healthcare provider.
Keep your chin up girl! You have made wonderful progress. This is just a speedbump along the way. Please keep us posted.
Starting Date: 3/15/15
Current Weight: 5# heavier since I stopped using fitday!