Preganancy related. It is undetected?

My period cycle is of 33 days average, I had period on 27th May later in June on 9th June and 23rd June I had unprotected sex, I missed my period in June which was supposed to come on 27th June. After that in July first 2 weeks my home pregnancy test showed negative. On 24th July my stick showed very faint 2nd line. I got my period on 25th July morning like full bleeding for 25th and 26th July changed two pads on both days, no cramping nothing. In my regular periods too I bleed for 2 days only. I did my pregnancy blood test on 4th day period which came negative. Still I have this fear that what if the test was a false negative or what it is undetected? Why did that 2nd faint line came on test kit. Did I really had period of it was implantation bleeding. Is it possible looking at all the date wise incidents that I might be pregnant or maybe not at all. I just need clarification on the same.