Dear Jessie,
it sounds to me as if you have a "trapped emotion" in your system. This can be the result from abuse you experienced, although your parents have changed,and indeed this is wonderful. Nevertheless sometimes these traumas get stuck in our energy system and commonly lead to "depression" or sadness. I highly recommend to you to go to the international EFT webside and download the free manual www.emofree.com . Then read through the first unit and then start tapping on yourself. On the acupuncture points illustrated in the manual, focusing on past experiences you made. I would work on what you told us here, although your parents have changed. It is in your energy system nevertheless. You deserve to lead a happy life. Know that many people experience this what you experience and it is no character flaw, it is a disruption in your energy system, which you indeed can "clear".