HELP!

i am beginning to get paranoid...could i be pregnant? i had sex in early January but i was less than 7 days after i had taken a late or missed pill. since then i havent really had much of a period...a drop or so of something that looks like a brownish mucus.... i have been on microgynon for several years and recently i havent really had much bleeding, but this is even lighter than usual...normally i would not think anything of it, but as i had taken a late or missed pill (thus less than 100% protected) and had sex abt 4-5 days later i am getting worried.

how long do you need to wait before a pregnancy test is accurate?