I just started a pack of birth control pills and i heard it takes 7 days to become effective. but i had unprotected sex on the 5th day. can i be pregn?

Too soon to know: If you are within 72 hour of sex, you may wish to take plan B and continue your regular birth control pills. Conception, as defined by the generation of a fertilized ovum, occurs within day or so of the sex. However, it takes about 2-3 weeks for the embryo to make enough HCG to produce a positive pregnancy test. Blood test may be done a day after a missed period. Home pregnancy tests should be done 4-5 days after the missed period. If the result is negative repeat the test in 4-5 days. Use first morning urine and follow instructions for the test carefully. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD. Practice safe sex. Get HPV vaccine.