Life is about choices. You can choose to be sad or happy. You can choose to be pleased or displeased. You can choose to be positive or negative. You can choose to be angry or satisfied. You have control over every emotion that you choose to feel. Everything is within your power and you have more control than you give yourself credit for.
Of course, you will automatically feel an emotion that is tied to an experience. The experience will bring up emotions based on other experiences and emotions such as loss, peace, excitement, past memories, etc. Once you feel the initial emotion, whether it is positive or negative, you have the choice to continue to feel the initial emotion or move past it and feel better.
When you are experiencing a negative emotion, you have the power to move beyond it. Believe it or not. The question is: How do you move beyond a negative emotion? The answer is simple: by focusing on a positive aspect of the experience. If you cannot find a positive aspect of the experience to focus on, then you will need to pull another experience/memory forward that easily brings you positive emotions and place your focus there. This will result in you dousing the fire of the negative emotion as the positive emotion takes over.
It will take long, hard practice for this action to become automatic, but it is not impossible. Look at your life as a work in progress. Take every opportunity to improve. Improve your emotions and you will improve your life immediately. Amen