Pregnant?

I had sex the 19th, period was supposed to come on the 27th. Since then, positive pregnancy tests ONLY when taken right in the morning, and very faint lines besides one digital. I had a blood test done 5 days ago and it was negative but went back today and got another done, since negative blood test, one positive test. It’s the 4th, so 16 days since I had sex. Is it too soon for blood test/pregnancy tests?? I had some bleeding yesterday but it started very light pink and is now dark black/brown, and the bleeding is not heavy and on & off, could it be implantation bleeding?????