I found the first 8-10 weeks of having Emma to be really stressful - I was so anxious, sad, kept crying all the time and every day tasks seemed impossible. Getting my son to school and back home again honestly made me feel about as nervous as getting up on a stage to sing in front of people. I didn't go to the doctor about it as I had PPD with Sophie and hated the stigma that's followed me ever since from health professionals.
I think having such big age gaps was harder than the 23 month one I had between Thomas and Sophie - having older kids that need to go places, and can voice their frustrations with you or the baby was super difficult.
I can't promise you things get easier, but just after Emma was about 8 weeks old I realised that I was less anxious, that the older kids were adjusting, and that we were all getting used to things. Now, I would say I am content and happy and have no anxiety or depression, we've all adjusted and it's so much better and easier. At the time it felt impossible to me that things would improve but it really has done so a million fold.
A newborn is hard enough as it is, but with an older kid it feels like you are being stretched thin and it's such a worrisome and exhausting thing to go through. Very stressful. I couldn't ever see how I would adjust or function but I really have a hold on things now and Emma's a delight.