Unprotected sex last Sunday night,
I had my period two weeks before that.

When do the symptoms start showing
and when is the right time to take a pregnancy test?
Thanks.

Not until I was about 7 to 9 weeks pregnant, believe me you wouldn't know yet.
Different tests work in different way's some not until a few day's after your missed period, other you can take as early as 5 day's before your expected missed period.
If you don't want a baby, stop having sex.

The soonest symptoms will show is 2 weeks from then, soonest test would be 6 days before your next period with the first response brand

i didnt know i was preg w my 1st baby until i was already 4 and 1/2 months. my 2nd, i was 2 months before i found out. no symptoms at all

One option would be to take the morning after pill asap.