PPD

I’m 14 months pp, not sure if it’s still possible to experience ppd ? I never felt sad prior to the first 12 months of my baby’s life. But for the last two months I’ve been experiencing sadness. Idk if it’s the lack of sleep he’s been giving me these past two months, idk if it’s the little to no support system I have, idk if it’s the problems I’ve been having with my partner. Maybe it’s a combination of everything. Not sure how to go about things. Any advice would be appreciated.