Thanks for your query,
Your scenario is quite confusing. Your last period was probably 19th april. So more chances of pregnancy
from unprotected sex since 21st april.Timing of positive pregnancy test also suggest this possibility only. You can go for ultrasound
scan which may help you a little in determining period of gestation . Final confirmation is done by DNA analysis which can be done even during early pregnancy by chorionic villus sampling
Hope it helps you..