As you noted, the problem may be that you don’t properly express your feelings. Perhaps you lack an outlet to do this. Experts generally say this is unhealthy.
Those who study emotions suggest making an effort to share your feelings. Talk to someone about your feelings, especially when you’re emotionally upset. If you do this more often then you may not experience a “build up” of emotions.
I’m wondering if you don’t express your feelings because you don’t know how to. Many people were not taught these skills. Maybe there’s no one in your family or among your friends who you feel comfortable sharing your feelings with. They are both possibilities.
If there are friends or members of your family that you trust then don’t hesitate to speak to them about how you’re feeling. If something’s bothering you talk about it. There is no reason to hold it in.
You may want to read about how to express or label your emotions. Two books that may be helpful are Fighting Invisible Tigers: A Stress Management Guide for Teens by Earl Hipp and Dealing with the Stuff That Makes Life Tough : The 10 Things That Stress Teen Girls Out and How to Cope with Them by Jill Zimmerman Rutledge.
Thanks for writing.