Seriously freaked out

My period was spose to start Oct 1st or 2nd . I had some spotting on the 2nd then nothing at all . My last period was Sept 4th and me and my partner had alot unprotected sex before my period and during it which was before my ovulation . And then he had to go away on Sept 8th for work . I know it's possible to have implantation bleeding during when your period is due .But I am not sure how it's possible for me to be pregnant unless the period I tho I had Sept 4th wasn't a period at all cause it was lighter then it normally was but still enough I tho it was one . O went to the ER last night cause I was having cramping and back pain . But the pee test they did came out NEGATIVE! My have never had any issues before ,my period comes every month like normal .so I am not sure what the frigg is going on but it has me stressed and scared . Anyone have have this happen to then or have any ideas? I have attached a photo of the spotting I had just the once on Oct 2nd below