There is absolutly no problem with your engine. The engine is so hard to get going because the oil gets thicker, the gas evaporates slower so it is harder to burn in the engine, and the energy producing reaction inside a battery happens more slowly when it is cold. So there is no problem with your car, don't worry, but if you don't start your car for a week and it is cold outside you may need a new battery,cause the cold will have killed the battery.