The last weekend of August/ beginning of September I had unprotected sex. And we didn't use any methods (eg. Pull out). My last period was almost 6 weeks ago, and I'm almost 2 weeks late. I've been having lower back pains, nausea, bloating , a little bit of pressure in my stomach area and really gassy , I've also been craving weirs foods and I'm tired. I took a pregnancy test last Thursday and it came out negative. Is there any explanation to this?