Weird Cycles Post Baby

So my daughter is 5.5 months old, and I have had 2 normal cycles and average periods, and now I'm going on 3 weeks late with some minimal spotting. I've been to the doctor and had a blood pregnancy test done, which was negative. I had been taking the pill, but I got nervous after my period was a week late and I stopped taking it. Anyone else having weird cycles post baby? We plan on TTC once she's a year, and I'm worried it's going to be hard since this is happening, and it took us a year to conceive my DD.