The world will be my oyster

I am constantly in a battle with myself these days. It is the confident part versus the insecure part and at the moment insecure is kicking some serious ass. I don't know why, in my later twenties, I feel more lost than ever before. I am continually questioning my choices and abilities and envy those who seem to go ahead and 'jump in' knowing they will succeed. I have no idea where my self-doubting ways have come from but I need to stop, re-evaluate what I really think about me and start thinking in a more positive way. Geez I sound so lame. But it really has come to a bit of a breaking point...either I start thinking positively or I might just end up somewhere I don't want to be.