Is it still PPD if your baby is 12 wks old?

Up until the last 2-3 days I was happy as can be but idk why the last couple days all of a sudden A wave of sadness set in...sad that I’m a single mom, sad that dating isn’t an option and I’m lonely when my baby sleeps and sad that my body is still 20lbs overweight... so weird how happy I was an now it’s like a switch flipped ☹️