Had sex about a month ago, this month my period came twice. First it was brown and had a light flow and lasted for 2 days then about a week or 2 after it came back with its regular color and lasted the regular 4 days which was in the early part of December. On Friday I ate an egg sandwich and after consuming it I experienced a sudden onset of nausea and had to vomit, I vomited 4 times in that 1 day. Since then, up until now, I have been having strong sudden onsets of nausea. I took a pregnancy test and it read negative, I took some gravol to suppress the nausea and it does not help. Could I be pregnant? How can I know for sure? If not pregnancy what else could these symptoms mean?