Confused please read...

I started bleeding the day af was due, it was a light period and only lasted 3 days. Normally I bleed for 5 days. Bleeding has stopped now but I have been having mild cramps, headaches and feeling nauseous. Is this normal? Is there any way this could have been implantation bleeding? Just been so unusual for me. I did a pregnancy test before af was due and it was negative. I don't know if I'm driving myself crazy thinking too much into it but just worried as we are flying out on holiday in a few days. Anyone else experienced this?