Chances are the one that originally infected you dropped off and you didn't even notice. It doesn't take long.

The little ones perch themselves on the ends of branches and long stalks of grass with specially designed hooks one the ends of their front feet fully extended to catch on the hair of passing animals. That is likely the way you got them both. If you're not looking carefully, you'll never even see them.

Plus, if you're hairy, or bitten in a hair covered spot, missing the bullseye is understandable.