Implantation bleeding or period?!

I've recently lost my virginity (in Feb).
I've been late on my period for 20 days now. My estimated period start date was 6/14. My last period was 5/13-5/18. 
We always use condoms, but on 6/15 my partner briefly put it in with out one. I don't think I was ovulating because i was supposed to start my period on 6/14.
Now from 6/26-7/3 I had some mild spotting the color was brownish/dark red and sometime almost black.
I've taken 3 pregnancy tests on 6/20, 6/23, and 6/29 and they all came out negative.
I just need some clarification so I can stop worrying. Please anything would help!