PPD/A 18 Months Later?

Is it possible for PPD or PPA to come on strong when my daughter is 18 months? I know I had it mildly when she was born and I thought it was better but now I'm questioning it. I've got this feeling in my chest that feels so heavy. It feels... empty. I'm not meaning empty as in I don't love my family or myself or anything like that.... I just don't know how to explain it. I want to cry all the time and it's not like I have a reason to be sad, but I am! Any advice?