Wanting last baby

I had my youngest almost 9 months ago, had my first ppd the 15-20 we baby danced all my fertile days and now when I nurse my baby my nipples are SO SORE and I have gotten a super strong armpit smell along with some nausea when eating I'm due to start a period in 4 days I've tested today and got a negative I'm just afraid that the period I had was like a fluke and I'm going to have such a hard time getting pregnant as we haven't been careful since her birth. I'm wanting our completion to the family baby and would love to have a fall season baby as I have 2 summer and 1 winter/spring baby(her bday is march)