Is it pregnancy hormones or depression?

I'm already a mother of one toddler (recently 3yo) and am expecting again in the next 2 months. I'm a SAHM and I've noticed I feel a bit 'off' - like I have a lot less patience and am more easily irritated by some of their behaviour. They are not unmanageable but I'm finding there's a little more generalised limit testing, disagreeable behaviour and mini tantrums from them. They also now seem to be experiencing what looks like night terrors while getting over a rough cold, which I'm praying is not longterm because I dread how to manage newborn sleep with toddler night terrors. Prior to this he has become a solid sleeper. I'm naturally apprehensive (within reason) about how going from one child to two will impact our current life, routines and family dynamics but I feel like behaviour that I would otherwise be more apt to handle is just grating on my nerves more easily. I also just feel a little bit more down and despondent overall (some due to pregnancy aches and pains, some emotional) but not tearful. Has anyone experienced depression onset by pregnancy? How did you recognise something wasn't quite right? Has anyone had depression before pregnancy and if so, in what ways was it different or amplified? I'm weighing up if this is just a difference in being pregnant with an existing child (so less time to self care) this time around, OR if there may really be an underlying problem which I need to get urgently addressed.