Why do I keep feeling bad when I face things which I thought I was over them ?

Because as you said you only thought you faced them when you really didn't, but there's nothing wrong with that. Try settling the situation (even if it means you're trying to settle it AGAIN), and if the reason for not succeeding is an outside factor (e.g.: someone else) then don't feel bad because you know you did everything I you could and that is what matters.

There are a few reasons in my opinion. One, you haven't properly made amends with the situation or never felt secure and satisfied with the solution or answer given. Two, forgetting is easy but letting go is hard. You may have felt okay and forget about it. However, think about what makes it hard to let go of those things. Third, the feelings that you experience when you face those things will always be there. That is OKAY. Although you have accepted that it happened, it will still feel that way. Just leave the past in the past and the memory, a memory. Lastly, you have different situations that connects and makes you feel bad. For instance, when you think about something then it leads to another things you felt bad about.

Feelings can sometimes feel unpredictable and uncontrollable. That is not your fault, you are very brave for facing things even when they are intense for you and you are allowed to do so at your own rate. If you are feeling bad you are probably relating to how you felt in that moment, it is important to honor that pain and accept it, even when it can feel difficult. You might carry a large burden but you are not a burden and you are deserving of care and support however you are feeling and however long the ago the "bad things" happened.