I ovulated June 2nd and had unprotected sex June 3rd. My breast became very tender June 5th. My period isn't due until June 17th. Could this be a sign?

Too early. This is too early to see signs of pregnancy, in most people. Wait a couple of weeks and do a home PG test. Check the different types and follow the guidelines, exactly, on the package. Make sure the kit is not expired.
Although you. might be pregnant. Normally a woman doesn't feel pregnancy symptoms two days after sex.
Not necessarily. You may be pregnant, although unlikely. However, if you are pregnant, it is much too soon for the pregnancy to cause breast tenderness. Unfortunately, it is too late for the morning-after pill to be effective. If you were not intending to get pregnant, you should have taken the morning-after pill within 48 hrs of having sex. Even better, you should take birth control pills and use condoms.