How do I heal myself to be happy again?
A lot of people seek therapy for exactly the reasons you mentioned--feeling that sense of being "trapped", being preoccupied with past events, and having low self-esteem. Of course, I don't know your specific situations, but I'll give you some general guidelines as far as how you can begin the journey towards accepting the past and finding joy.
When we have thoughts of feeling trapped or when we fail to love ourselves, this is always because of the thoughts that we tell ourselves (known as our "self-talk"). We can become so accustomed to having certain thoughts that we don't know notice them. However, so long as we have thoughts that lead to negative feelings, we will continue to have negative feelings.
Changing how we think about ourselves, others, and our past experiences don't happen overnight. It is a major focus of Cognitive Behavioral Therapy, and the first step is to start paying attention to what we are telling ourselves. Some clients do this by using a thought log. Therapy can help individuals start to notice patterns in their thinking. The next step is to notice how that thinking maybe maladaptive or irrational. Are the thoughts you're telling yourself based on facts and helping you live the life that you want, or are they presenting an obstacle, and are they unfair to yourself? The focus is then on practicing using new self-talk (positive self-talk), replacing the irrational, maladaptive patterns of thinking with cognition that promotes growth, acceptance, pride, etc.
Again, I don't know what you're referring to when you mention the past and feeling "damaged". I don't know if you have experienced trauma, have been in a painful breakup or lost someone close to you--or something completely different. The important thing is that we need to deal with the past. Yes, some level of distraction can be helpful at times, but part of good self-care and talking about our thoughts and feelings. Having a therapist who is unbiased and able to offer an outside perspective and who will offer confidentiality could provide a safe space to begin to heal from whatever past even you are referring to.
It can be tempting to want to push the past away and pretend that everything is fine. It is also common for people to tell themselves that they will never "get over" the past and that their lives can never be the same. We can give ourselves infinite excuses to avoid dealing with what is painful. Something though gave you the willpower and courage to reach out and admit that you are struggling. You also have some hope as well, as you believe, at least to some degree, that things can improve. There are no simple fixes for dealing with a challenging past. It does take work. However, I can tell you that in the 10 years that I have been working as a therapist, most clients who commit to therapy and challenge themselves to confront what may be uncomfortable do notice significant improvement.
I'm also a believer that there are times when psychotropic medication can be helpful. While I do not prescribe it myself, in some situations, in combination with therapy, it can reduce depressive symptoms more quickly (if depressive symptoms are in fact what you are experiencing). However, when our mental health is impacted by past events, at some point we really need to work on addressing those. Therapy can also teach us how to implement coping skills into our lives, which can help reduce the anxiety and discomfort associated with confronting those past situations.
I strongly encourage you to give therapy a try. I would be happy to work with you, and please feel free to let me know if you have any questions about therapy. Take care of yourself, and have a good rest of your weekend.