What’s going on?

So my period has always been super regular since having my son 7 months ago. My husband and i would like another baby, but we’re not really trying, just not preventing lol. It took us a long time to get pregnant. We had sex once 8 days before my period was due, and now I’m late. I thought I could be pregnant, but all test are negative. I know of course you can get pregnant any time of the month, but it seems so late in my cycle to conceive. Wondering where AF is!