13 days late

So I'm 13 days late on my period, I have sex regularly with my boyfriend and never use protection just withdrawal. My boobs have been extremely sore especially my nipples. I have had headaches more than normal, extremely tired all the time & some nausea at times. I seem to also smell every little thing and it makes me feel pretty nauseas at times as well. I took two pregnancy tests at home at around 4-5 days late and got a urine test done by the doctor 2 days ago and they all came back negative. Any advice or clue to what else could be going on? 
UPDATE: I am now 15 days late and having mild cramping with light nausea almost all the time for the past 2 days. I'm also having some white discharge. Still no sign of AF