Late period, negative preg tests?!

I’m so confused about what is going on with my body right now. My period is now a week late, but I’ve got negative pregnancy tests. I have no symptoms of anything right now so I have no idea what is going on. Is it possible to still be pregnant/do I need to still keep testing? I feel like I’m wasting money at this point as it seems impossible to be pregnant based off of when I had sex last month, but the only other time my period has ever been late was when I was pregnant. If anybody can shed some insight I would be so grateful.