possibility of pregnancy??

I am a newly wed and we are trying to have a baby. last month my period was a day late and I only bless for 2 days then had very minimal spotting 2 days after and that was all. I took a pregnancy test the day after my 2 day period and it was negative but I'm not sure what's going on with my body. I usually have 5 to 6 dat periods and the shortest I have ever had is a 4 day period. I still had cramps and other period symptoms. any ideas what would cause me to have this? please help!