Nothing matters it seems

I'm feeling overly depressed. I've tried talking to my SO and it seems like he just doesn't understand or doesn't want to. Every time I've expressed how I feel, it just gets swept under the rug and he pretends that it doesn't exist and everything is fine and dandy once I get done telling him. I've had issues in the past with self harming and suicidal ideation and he knows that, but he acts like it's a big fucking joke or something like I'm not being serious with him. It's been a while since I've had any feelings like that, but lately I don't even know how to explain my behavior. I'm almost 5 weeks PP and I think it's depression but I'm not sure. It comes and goes in waves. I just really feel as though I'm not being taken seriously and that no one is listening when I tell them what I'm feeling. I'm just going to fucking disappear one day and no one is going to know what happened or why because no one freaking listens to me when I actually try to reach out for help.