What Causes Irregular Periods With A Negative Pregnancy Test?

Last month i did not have a normal period,if what i had even was my period. I thought i might have been pregnant, but the test was negative. I still have not had a normal period and continue to have nausea,cramping,nipple sensitivity,and other sumptoms that i have researched and have seen could be pregnancy symptoms. I am wondering if there is any way i may be pregnant still.