I just don't know what's going on...

My last period ended on the 19 of last month, and I was supposed to get my period on the 12 of this month. So I haven't gotten it. My fiancé and I have not used protection, not even as much as withdrawl (sorry if that's tmi lol). My breasts have swollen, I've been having cravings, certain smells are bothering me, I've been nauseous for weeks and vomiting on and off. But I've taken 3 pregnancy tests (1 clear blue, 2 cheap ones from a local store) and all have gotten negative results...I'm not sure what I should do... Any advice??