Most babies dislike Tummy Time at first, so it takes a little patience.  Try some tummy-down holds like the “football hold” and the lap soothe, instead of always propping him upright on your shoulder.  This may get him accustomed to the position.  Check out this website for more tips from Pathways Awareness: http://bit.ly/8IhuuF.  They also have a unique calendar with activities to foster your LO’s growth: http://bit.ly/5lGkTm.