No advice about 3 plus (hopefully in a few years 😇😊
but I really unexpectedly kind of felt this way while pregnant w no.2. Did you feel that way for no. 2? It may be a similar thing not sure but in case it is helpful here goes. My ds2 was very much wanted and planned and it kind of threw me that I felt that way. Ds2 is now 5 months and it was totally fine! Some parts so far have been rough but you get on with it and soon it will be the new normal. I suspect you just worry because you love your existing kids and want to make sure you can do right by him/her/them as well as the new baby. So I think
in a way it is only natural that you worry. But you can't do anything about it now so you may as well try and put it out of your mind a little for the moment. Tho talking to DH, my mother or friends about it did help me feel better about it while still preg. Happy and healthy 9 mos!!