What Causes Inconsistencies In Menstruation?

hello i just finished my period 4 days ago but now am bloated cramping back pain headaches moody same as if i was getting it again but i just got off took a home test it was negetive.but for the past 3 months my period has been crazy it comes 2 days and am done it comes 27 days got it 32 days and i am really trying to get pregnant .