what is this feeling?

tightness in the chest
upset stomach
can't sleep at night
headaches
tired all the time

i think it's stress. generally i don't feel stressed out but i think when it happens it manifests itself physically (as in me thinking i'm sick but i'm not). but why? why am i stressed?

"as for me, i am poor and needy,
but the Lord takes thought for me,
You are my help and my deliverer,
do not delay, o my God."
psalm 40:17