HELP me get a piece of MIND!!????

So I normally get my period the first week of every month. I haven't had a legit period since April 1-7. When I say legit, I PMS'ed and bled consistently for 7days. I saw some spotting the last week of April 24-26 maybe. It wasn't heavy and didn't last long because I had sex with guy #1 April 28ish (we used a condom). We had sex again May 2nd and May 15 (with protection). 

I noticed some spotting May 13 but it went way and then came back during sex May 15. I had sex with guy #2 May 17 (with protection). Guy #3 (Big Mistake, 1 night stand) May 28, didn't used protection, from what I remember he didn't cum inside of me but I took a Plan B pill May 30. 

I took a pregnancy test May 30& May 31 both negative. I though to take them because I realized that I haven't truly seen my period in May. 

I had sex again May 31, (unprotected with my long time, on again off again BF) he came inside of me thinking that the Plan B would still work the day after. We did it again June 5. 

I got really sick this past weekend and ended up at the er, I happened to just ask them to do a pregnancy test and the test was negative..

But I was bleeding a little today, 

I read online about implantation bleeding& I'm unsure if it's my period or implantation bleeding. It honestly doesn't seem like my period because it was a lighter red..

Then I put a tampon in, thinking it was  my period and the blood inside was brown. 

My question for the readers is,

Where do I go from here? 

Do I wait to see if I keep bleeding and then take a test? If I'm pregnant, what guys can I pretty much rule out that wouldn't be the father?