sore uterus

Has anyone experienced a sore uterus before bfp or period? I'm 3 or 4 days late and my uterus feels very sore. Like I pushed a cart at Cosco and it kinda hurt. Normal things like sneezing and just regular life sometime makes it hurt. Otherwise it's just a dull soreness or cramping. I haven't done anything active or abnormal to cause it to hurt. I'm just wondering if it's a sign of af about to show or if I'm pregnant. Took a hpt a couple days before my period was due and it came up negative. The soreness is making my lower back ache a little too. Any ideas of what t is?