When can I rule out pregnancy?

I had a very light period this month. It was on time. However, it was verrrrryyyy light. Almost no blood comes out when I stand, sit, or walk; but a lot flows whenever I pee. I never really had heavy periods but they werent as scanty before, too. I could fill up one whole napkin. It lasted for four days. I was worried so I took a pregnancy test on after the last day, which came out negative. It didnt calm me down however, as I still felt weird. I dont know if i imagined it, but i was tired, my head hurt a lot (which has always been the case for me -- but i blamed my poor eyesight sometimes). anyway, because i was still thinking about it, I took a second test (this time, it is around 12 days since the last day of my period -- 1 week since my last test) which also came out negative. Its been 2 days since then. SHould i still worry? Technically, I didnt really miss a period yet. But im just crazy paranoid.