I had an intercourse on the 5th oct. After which I felt sudden nausea. I planned on doing a pregnancy test but then since my periods were due on 21st oct I planned on waiting. I got my periods today (18th oct. The flow is heavy, red and with severe cramps. Can it be implantation bleeding or just normal menstruation? Are there chances of me being pregnant? I don't come across other symptoms of pregnancy apart from nausea, tiredness.