I fell pregnant when my now 15 month old was 8 months. It was a very hard pregnancy, I completely feel like months 9-12 was wasted by morning sickness, bleeding, non stop hospital stays and to top it off my baby boy was born at 21 weeks on my dd first birthday! So her birthday was ruined and the time before that. And I ended up in hospital for an extra 2 weeks as I nearly died
Now my story is extreme and I never wanted 2 under 2, it was a surprise, and it was never meant to be anyway :( Anyway my point is, you never know what's going to happen, my first pregnancy was textbook perfect. But the next well... even if I didn't end up giving birth prematurely I was told at 33 weeks I would be admitted into hospital for a month then c section.
As I look down at my 15 month dd sick with a cough my heart breaks if I wasn't able to be here with her. Everything happens for a reason.
As long as you are prepared for every possible outcome and situation, then your decision is decision and you wouldn't be crazy, lots of moms have two under 1, two under two, and love it and once the early years are done, it's meant to be amazing.
But yeah 4 months, babies are easy, it's toddlers that will make you rethink your decision haha
Best of luck in whatever decision you make xxx