4 months PP

Here’s the story:

I had my boys at 32 + 2. They were born July 3rd, 2017. Im SO in love with them and absolutely adore being around them. Well lately, 4 months later, I’ve just been feeling really sad and frustrated and just little things make me upset. Now the thing is, as soon as I’m with my boys, I start to feel better and then a few minutes later I feel perfectly fine. It’s like they’re my remedy for my sadness and anger.

I guess I’m just wondering if it is still possible to get PPD after 4 months? And would it even be considered that