My 5 month old son did a new thing this weekend. Twice when he saw my dad (who he sees about once a week), his face crumpled and he started crying. He nearly leaped into my mom's arms when she came near (he gets to see her much more often because she doesn't work). Then today at the vet, the doctor took one look at him and he started bawling! He has always been very easy going and anyone could hold him. Is this stranger anxiety? But only towards men? Normal for 5 months old?