How do you even know you're pregnant at this point? The egg may not have even implanted yet. As per your question, if you are pregnant, they measure from the date of your last period which is about 2 weeks before any chance of conception. Therefore, when you miss a period, you're already about 4 weeks along. Symptoms start to occur about the very same time - 4 weeks - and it's about the same time you'll get a positive test result. There's no almost no way to know anything until then.

You wont know until another week and a half or so.

You wouldnt know that you got pregnant a few days ago, there could be a chance that you did concieve a few days ago but you wouldnt be able to find out for a few weeks. Are you self assuring yourself that you are pregnant or did someone actually tell you this? Yes any time having sex carries the risk/blessing of becoming pregnant but you do not simple become pregnant for having sex.