It’s great that you are reaching out for help, now you can start the change.
Anger can be a part of personality, I.e. is there since adolescence. In such persons stress may aggravate aggressiveness.
But anger in persons who have been calm otherwise is mostly due to mental problems like depression, anxiety, addictions and others.
Next Steps
Anger (if not manageable by self) requires consultation with a psychiatrist or a counsellor.
Health Tips
Anger can become a habit and cause disastrous consequences in many areas of life like relationships, work, health and others