Depression

I've been treated for depression before but moved to the other side of the country, changed my life, met a new man, moved on... But now at 36 weeks it creeps back... Worse than ever... 
I have an older son and feel like that is all that keeps me here sometimes... I just wish I was strong enough to end it but can't do that to him. It doesn't take much to tip me back there... 
I feel like I just can't be happy about this or anything and this new little guy will just be another reason I can't end it... 
Some days I do feel happy... But others I just can't cope. 
Is anyone else feeling the same?