You definitely want to bring this condition to the attention of your contractor before the first year is up. Since your house was built during the winter it probably was exposed to considerable moisture. When the drywall is applied before the moisture is driven out of the wood by the central heating system it will naturally shrink as the moisture goes out over the next year. This is what you are seeing. As the lumber shrinks, the drywall must contract by the attachment points (screws).
Ask your contractor to examine the conditions and he will recognize that the house was not adequately dried before the drywall was applied. He should make repairs as needed.