Have you cracked any of the apples open to see if there is a worm inside? Eventually you will need to post a picture of the damage to get better help.

Coddling moth or apple maggot fly would be my guess of the problem. You might google search it and see if that is what the damage looks like and then treat for whichever one or both that are the culprit.

...as for the biennial bearing, if you thin the apples the year it fruits, you will prevent it from expending too much energy on the current crop and resting the next year. then it will fruit every year.