Feelings of uneasiness, unsure & not good about myself. Is this common during pregnancy?

I'm in week 18, and recently, my mood seems to swing towards feeling uneasy, being unsure, and not feeling good about myself. It comes and goes, and I don't feel like that when I'm in my 1st trimester. Just wondering if this is common during pregnancy and will eventually go away, or it could lead to more serious issues such as postnatal depression? Anyone can sure their experience?