I Had My Period For September Already And It Came

I had my period for September already and it came on time, however day 2 (which is typically the heaviest flow day) was very faint and light as if it were more like day 3 or 4. Now a week later I am very lethargic and tired all the time. I have two kids so I have been pregnant before and extreme fatigue has been a pattern for my pregnancies. Despite getting my period I took a pregnancy test a day or two ago and it came up negative. I'm aware my fatigue and other symptoms could be a result of a multitude of things but is it possible in my circumstance to be pregnant? Did I just test too early? And if so, what was the meaning of getting a period?