Late diagnosis PPD

Erin
Has anyone been diagnosed with PPD later than what is typical? I'm four months postpartum and I feel like I've made excuses for the way I've been feeling until this point where I'm out of excuses. At first I thought it was because I was sleep deprived. Then I thought it was the mini pill I was taking as birth control because I was sensitive to birth control in the past. So I changed to what I was previously taking. I blamed hormones when i stopped breastfeeding. My baby is sleeping thru the night and I'm still feeling like the baby blues just aren't going away. It's not serious, just constant blue feeling. Occasionally I feel better but the days that I just want to stay home and cry is more than the days I feel good. At this point I'm not even sure if I should call my OB or my pcp since I am 4 months Postpartum.