Crying out for help!

I'm 20 years old and just had my first baby boy he's 6 weeks today. I've struggled with depression since I was 15, I managed to get it under control not so long ago but since having my son I have been so so low. the baby's father sees the baby 1-2 times a week and has him with my presence for about 2 hours. today ive hit the bottom, my baby is really hard work and screams all the time, I've told my mum I can't cope, ive told her my thoughts that go through my head and she told me to get a grip and that I'm disgraceful! I can agree with that though, I've just walked out and left my son with her I'm freezing in the cold walking and walking and I dont have a clue where I'm going, all I know is I'm lost and broken. I'm trying so hard to be a good mum, to be a good person but I'm failing miserably