Heaven has been away too long

I feel so intimidated by people. I'll be feeling pretty confident about myself, and like who I am, but then someone comes along and then all the confidence I had disappears. Not only do I feel like I'm good enough for other people, I never seem to be completely happy with myself. I can be skinnier, smarter, have a job, etc. I'm constantly trying to form myself into a definition of "perfect" but even then I don't know when I can finally say I've reached it. All I know is that right now, I'm feeling kind of low about myself, and I don't really know what I'm supposed to do about it. Diet, study, apply for jobs? I feel like I'm under alot of unnecessary pressure. Pressure that I'm just creating for myself that causes me to constantly stress out. This isn't something new to me though, I've been doing this for as long as I can remember. I just don't know how to be happy being myself, when I constantly feel the need to improve in every aspect about myself.