Possible to be pregnant after a 7 day heavy period?

I was looking this question up on google and came across a couple forums where women had experienced this, apparently they didn’t have enough pregnancy hormones to prevent their period from coming but were still pregnant and completely healthy. But I wanted to hear it from some of you lovely ladies if this has ever happened to you? I’m wondering because all pregnancy tests were negative last month and then AF came four days late, however no matter what I eat I’m nauseous and/or throw up, I’m gaining weight when I should be maintaining it. So just wondering if it’s ever happened to any of you..