Meaning is inherently subjective. You can no more have an objective meaning than you can have an objective opinion. All of our values are self-determined.
I've been in the state of mind you're in, it's not nice. But I guarantee, given time, it becomes clear that like any view on reality, a state of mind is all it is. Existential depression is common in people who think everything through a lot (too much, people keep telling me) and at it's best, it's a way to learn and grow.
I guess it's harder when you don't think there's anything after death. But even if there isn't, the nothing that's beyond the only thing that actually is i.e. our experience alive, here and now, shouldn't be important. What's important is what you value in this life. Do you love anyone? Is there something, somewhere, someone you want to be? Is there anything in the world that's important to you?
If there is, then you've found your meaning already.
If there isn't, then you've found the real source of your depression instead.
Because the question is never really whether there's meaning in life itself, but whether there's meaning in your life.