"How do I know if I'm pregnant? My first period was three months ago, …

"How do I know if I'm pregnant? My first period was three months ago, and it wasn't my first period. It happened a month ago, but now I feel like I'm getting ready for my period. A test will be done soon. All signs point to pregnancy, but on the test, there is only one result that says "negative". It's been 12 days since my last period, but they say it won't happen in six months."