PPD or just freaking tired?

Hi mamas, I know we are all tired. Like really tired. And being in quarantine and stuck in the house for weeks on end with an infant and (in my case) a very chatty, busy, playful, attention-seeking 4-year-old has been harder than I thought it would be. My LO is 4 months old and pretty sure she’s hit the sleep regression that comes with this age. Last night I got 6 hours of sleep, but had to get up to nurse and tend to baby 3 times. We’ve had this kind of sleep off and on for the last couple weeks. Today I feel so awful, down on myself, crying in the bathroom, overwhelmed, weak, and frustrated that I can’t get anything done...just incompetent. I don’t have the energy to play with my oldest the way I want to. I find myself just watching the clock for when I can put my youngest down for a nap. I don’t have the energy to respond to friend and family messages. Now I kind of feel this way most days (minus the crying), but can generally get through the day being a positive person and laugh about my downfalls. But when I get so little sleep it really puts me over the edge. Is this PPD, or am I just tired? Would medication even help or should I just try to push through until baby is sleeping better and then see how I feel? With my first, I’m 99% sure I had it but didn’t know and never did anything about it. This time around I felt great in the beginning, but the last couple weeks have gotten me down.