Consistent feelings

I often feel some negative feelings without any specific thoughts. Two main feelings are the stressed feeling in my stomach or a hollow feeling in my chest that is similar to self-conscious or lacking of confidence. Most of the time I can’t observe or notice specific thoughts trigger these feelings, but they are just there all the time. I am not sure if it is a natural state that I developed over the years, or from some unconscious thoughts that I am not aware of. How can I change this? or slowly alter these into neutral or positive feelings?