Pregnancy symptoms but negative HPT 7 days before period

Patient: On days 15, 16, 17, 18 of my cycle I experienced a heaviness/cramping in my lower abdomen, quite different than menstrual cramps. Also, I never get premenstrual symptoms this early before my period. The heaviness, bloating, and cramping have subsided. I am not 6 days before my period and I do not have the normal PMS that I usually have. I now have slightly heavy feeling breasts that are also tender to the touch only on the sides, on and off nausea, tiredness, and mild cramps. I took a HPT yesterday (7 days before my missed period) and got a negative result. Is there a likely cause of these symptoms that I am experiencing?

Symptoms: Lower abdomen cramping, nausea, decrease in appetite, scant cervical mucus, sore throat