Of course it is your low self esteem, but you have to go deeper than that. What is causing the low self esteem? Your beliefs of course. At your core you believe that you are unworthy (which I relate to) because of what OTHER people have told you through the years (the people you are attached to- like mom and dad and siblings, etc). You certainly did not come out of the womb believing you were unworthy, but somewhere along the way environmental factors kicked in and formed negative beliefs. But this is the thing- beliefs can CHANGE! What you believe about yourself can come from you. Decise what you want to believe about yourself and begin living with the intent to BE those things. Positive affirmations help a lot too. This and good solid exercise is what keeps my head up.