Early period

Hello fellow Glowies! My husband and I just started trying for our first child last month. I was on the pill for years prior and have been off now since January. My periods have always been a tues-sat. This month it came two days early. This has never happened. I took a pregnancy test 4 days before what could have been my missed period and it showed a negative. Maybe it's my body trying to adjust not being on the pill? But since January being off the pill, this hasn't happened. Any thoughts as to why this may be?