Quick disclaimer, I’m a dog person and have a pretty limited understanding of cat behavior.
I think the feelings you’ve described of being very overwhelmed and at times even resentful of the impact on your lifestyle, as well as worried you’ve made the wrong decision are so so normal. I have three dogs and felt all those things with each one (and probably will feel them again with the next) but I wouldn’t trade my babies for anything. That said, being just a few days in is way too soon to throw in the towel. I would give it a minimum of three months (time frame explained below) for you and the kitten to adjust to each other and develop your routine before even considering trying to rehome (which I’m not sure you’re even putting on the table…but just in case). As part of that, it is okay to take time to yourself away from your kitten, especially as she gets older. With all my dogs, their training included time in their crate or baby gated in another room even when I was at home because they need to be able to cope with downtime/being on their own, and everyone (including parents of human babies) needs a break sometimes. If you’re not comfortable leaving the cat alone, is there a trusted friend or family member who could come entertain her for a little bit every once in a while?
That said (and this is where my disclaimer kicks in), I would definitely NOT recommend getting a second cat. My understanding is that while cats are easier to socialize while they’re young enough to grow up together (as are dogs), they are also in general more difficult to socialize than dogs because they aren’t pack animals. In addition to the increase in logistical complexity with multiple animals in a home, socialization requires time and energy, and if you are already overwhelmed, I don’t think you’re in a place to provide that. With my current dogs, I brought a 4-month puppy into my home with a senior dog, and it took us about 3 months to settle in with each other and develop a routine. Right once we’d gotten settled with each other, she hit her “teenage” years and we had another 3 months of chaos. While my senior dog is pretty ornery and would prefer to be left on his own, puppy #2 loves playing with other dogs and wanted nothing more than for him to play with her at home, so when she hit 1.5 years, I decided I wanted to get another dog closer to her age/energy levels to give my senior boy some peace. I fully expected another several months socializing all 3 dogs, but especially my senior and puppy #3. In reality, after I adopted a 10-month old boy, he and my senior dog adjusted seamlessly in about a week, while he and his sister (neither of whom had shown any reactivity to another dog previously) had about a month where they wanted to attack each other any time they were in the same space, and I ended up having to work with a trainer to help me socialize them, and it took us a full 6 months to really be at peace with each other no matter what. They now love to play together and do keep one another entertained, but it was a lot to get there, and I’m sure you can imagine I cried and questioned my choices just about every day during that time period. I even had to resign myself to the possiblity of needing to keep them separated for their entire lives because I felt I’d made a commitment to both dogs and couldn’t go back on that even if it didn’t work out like I’d envisioned. Bottom line, you can never exactly predict how two animals will do together, and there have been just enough responses here to the effect of 2 cats = double trouble that I wouldn’t chance it.
Best of luck to you for things to settle down quickly. While my time frames from my dogs may not be the most reassuring, hopefully they illustrate that it does always get better, even if that feels out of reach today…especially if you stay committed to training. Also, my guys are all special needs, with puppy #2 having some neurological damage from a traumatic head injury before I got her, so my time frames are probably much higher than average.