Pregnant?

So, my cycles are usually pretty regular. Around 28 days. I am currently on cycle day 31, nauseous, tired, and having headaches. We weren't trying to get pregnant but we weren't exactly avoiding it either. I took a test the day my period was supposed to show up but it was negative. Could I still be pregnant? I was planning to take another test Wednesday if my period hasn't shown up by then. Anyone else experience this?

Side note: I have a 10 month old son and I found out I was pregnant with him 2 days before my period was supposed to show up.