What’s the deal?

This is my calendar currently….i was expecting to start my period last Friday, October 11th. And it still hasn’t come. I’m 10 months Postpartum and haven’t had a late period since I started having periods again. (The last 9 months I’ve been right on schedule). My husband and I literally just started not using protection about 5 weeks ago, as our plan was to start trying when my daughter was in her crib. It also took about 2 1/2 years to conceive my daughter so we thought it wouldn’t happen right away. But i have yet to start my period and have taken 4 tests that all came out negative. I took tests on October 7th, 11th, 12th and 17th. What’s y’all’s opinion on what’s happening? I don’t want to jump to the assumption that I’m pregnant and get excited before getting a positive result. But I don’t want to schedule a dr visit just for them to tell me I’m late. I guess I’m wondering if it would be possible that I’m pregnant and just not far enough along to get a positive result at home.