Implantation bleeding?

So lately I've been really moody and emotional, nauseous ALL the time, but haven't gotten sick. My appetite comes and goes. I've been really fatigued and lazy feeling. I (thought) had a period a week ago. It lasted the normal length but it was mostly light. One day I wouldn't bleed at all, the next I'd be bleeding like normal. I figured all my symptoms were from stress. A friend of mine mentioned implantation bleeding. I googled it like I always do and the dates it gave me made sense with a time I had unprotected sex with my boyfriend. It said it can last up to 7 days, and my "period" was 6. I took a test but it was negative. Anything similar happen to you guys?