I had protected sex on 29th May with no ejaculation. The first HPT was on 14th June which was negative, a day after on the 15th I got my periods which lasted for three days. Two negative tests on 28th June and 1st July. I did not engage in sexual activities after May 29. Today is 19th and although my period is due today I still don't have my periods and a pregnancy test revealed a faint positive line. I had an ultrasound on 4th July which did not show any pregnancy. My question is 1. Was the period implantation bleeding? 2. If I was pregnant, would not the ultrasound have detected it? 3. Why did I have three negative tests on 14th June, 28th June and 1st July respectively and then have a faint positive line today i.e. 19th July? 4. Shouldn't the positive line be darker considering it has been around 49 days since my last ovulation on June?