Nausea, late period. Out of the blue.

I am 28 yrs old and on 2/14 i experienced extreme nausea and my menstrual came on the same day (I never experience nausea and vomiting during menstrual). Menstrual went off in 3 days but nausea and vomiting continued for almost 2 weeks. I've had no appetite, and the little things I did ate or drink made me nauseated and vomit. Within those two weeks I started discharging brown stuff and that lasted for about a week and a half. Ive been having stomach cramps in the lower part of my stomach every so often also. My menstrual for this month is late which was set for 3/14. I was told it was acid reflux when I had an endoscopy done, but now my menstrual is late. Could the vomiting and nausea for the 2 weeks interfered with my menstrual and cause it to be late or could it be pregnancy(there is a chance) but Ive taken at home test which was negative. (Also, Ive never had any heartburn issues or GI issues ever) These symptoms came out of the blue.