Treats are not the only praise you can use. And since it's only been day three, expect to use those treats for a little while longer. You really want to get it in his head that come means AWESOME things. Does he play with toys, another great thing to use as a reward. When you eventually do start phasing treats out, start by getting them off your body, so keep them a couple feet away, recall, yayayayayay to the treats and reward. Keep getting them further and further away. You can also play with alternating rewards, play, praise, treat, treat, play, treat, praise, etc. And you will always want to do reminder training. Especially in new areas, I will treat every time I say come no matter what.