Could it be?!?!

So I was due to start my period yesterday (18th). However, on the 14th I started spotting for the next five days. This wasn't like a period at all. I had mild cramps the first day and after that there was no other pms-like symptoms. I took a pregnancy test on Tuesday, but it was a BFN. I'm hoping I just tested too early. Lately, I've been getting waves of nausea throughout the day, I'm starving all the time, increase in urination... what do you guys think? When should I retest?