A few comments:
– If you were unable to take AP classes because you transferred into a school then that must be addressed by your guidance counselor in his/her letter of recommendation to colleges. It is definitely not something you should explain.
–My guess is that with your weighted GPA of 3.1/5 (from another post) that you simply did not qualify for other AP classes in your HS at this time.
–I recommend you spend your time and energy doing as well as you possibly can in your actual HS classes.
–In another post you said you were taking two APs in school this year (Comp Sci and Environmental Science) – now you are down to one? http://talk.qa.collegeconfidential.com/what-my-chances/2196014-do-i-have-a-chance-of-admission-after-poor-frosh-and-soph-grades-and-upward-trend-in-rigor-p1.html What happened?
–If you have extra time get involved in ECs you care about. Colleges are looking for people who are involved in their school and or community – not just academic drones.
–To be clear self-studying does nothing for you in terms of college admissions.