Is this implantation bleeding or has my period come early?

I took a plan B about a week ago. 2 days ago, I had a gush of water like liquid come out and when i went i check it out, my undewear was soaked. The liquid was clear. When i got home later that day, there was some brown stuff. Like dried blood. When i got into the shower the following night, i was bleeding but it was like water. I have been bleeding like that for the last 2 days. Yesterday i developed some really light cramps and got a really sharp pain in my neck. My period was supposed to start next week. And my last one ended on the 6. The last day of my ovulation was 9 days ago. This was took thos morning.

Any insight?