2 Week Late Period

So tomorrow marks two weeks late I'm hoping I'm pregnant but I checked on the 13th of this month and it came out negative I won't have a doctors appointment till 28th and I'm just wondering if anyone else has gone thru this . . I'm so confused like what could be wrong or if I am pregnant why do I keep getting negative its so heart breaking because I Want to have a baby so bad and I feel different but I'm worried its all in my head only because of how bad I want to be . .