PLEASE HELP Doctors pregnancy blood test

Hey so a little bit ago I did a pregnancy blood test because glow told me I was due for my period on Monday but my period comes the start of the month of the end of the month into the start, I normally get really bad periods I have endometriosis I did the blood test on Thursday got my results and he said I wasn't then a few hours later I got my period I bleed not to much less than usual but like medium pain I could deal with it normally I'm in bed with visits to the hospital screaming in pain, I've been having weird light cramps but I'm on ovulation and never had them cramps and I've been peeing 4-5 times and I don't drink any more and normally I pee like 1 a day maybe twice and when I need to pee I start busting and more constipation, a bit of insomnia but I don't know if it's related

But I just have a feeling to take a test plus my fortune teller which is right on some thing told me I'd be pregnant by Christmas after I see a doctor which I seen a doctor a few weeks ago and Christmas is coming up is there a chance that maybe I ovulated late or implantation was late and it wouldn't come up in the blood test ?