I only know the implantation date, how should i count my pregnancy weeks from there. i lastly had my periods in march 2020 and implantation happened on the 16th n 17th of august 2020?

How does one know?: Implantation is when the embryo attaches into the uterine wall. There is no immediate sign of that happening. Nothing in nature signals the event is happening. Some women see a bit of vaginal spotting after implantation. The blood and urine HCG soon become detectable after implantation. But all dates are estimates (exactness doesn't matter). Can start counting 3 weeks before "implantation."