What Causes Light Spotting And Delay In Periods?

Hi i had a period last month but it only lasted for 2 hours as my periods have never been irregular and i am due my next one in 5 days i have done a pregnancy test last month but it came back negative. I am a little worried as a little bump sort of like a baby bump has started formaying. I'm just wondering if this isn'y pregnancy wat could it be?