First off if it is the runt then it might need additional attention to ensure that it gets stronger. Looking up and moving around in circles could be because it is looking for its mom or it could just be confused. Maybe try to ensure it gets enough of its mother milk. When it gets to six weeks try to supplement the mothers milk with additional food. But keep an eye on it when it is walking and moving to see if it has any issues with its balance. You might need to seek medical attention later on if it continues to have issues with its head. But if it can walk ok and move around ok without falling over, then it might grow out of it.