If i am two weeks pregnant now and had sex on the 4th this month does this mean that's when i conceived??

Not really: If a woman knows when she ovulated, then she conceived that day or within the 2-3 days after ovulation (because the egg usually won't last longer than that). Otherwise, a woman is already 2 weeks pregnant (by definition) when she conceives (when sperm meets egg). An 8-11 week ultrasound scan can estimate the conception date to within a week.