How come i cant break out of this depression.....?

I know i should be happy because im pregnant and having a healthy pregnancy,..my babys father walked out on me almost 4 weeks ago and ever sense i cant smile or even think about being happy i feel alone and empty...almost like im alive but not living people r judging me and talking about me now like saying im need to suck it up and stuff i dont need to hear that from anyone unless they have been in my position how can they say anything?...i just dont know what too do,how could he just leave me with his child goes to show how things are these days.