I don't know what to think?!!!

Today I am currently 4 days late on my period.. I have been feeling nauseous, tired, and my breast just started to get very sore and big but I am still getting negative results. My doctor recommended to come in tomorrow (Wednesday) to get an ultra sound to take a look at everything if my period doesn't come before then.. I'm so nervous that I will get my period! This is my 3rd month trying and I was on birth control for a long time before this so I'm just not sure if my cycles are crazy off or if my at home pregnancy tests are not detecting if I'm pregnant or not?!