I had sex one day before my predicted ovulation day and i have been on birth control for the pass three weeks. today ( two days after sex) i saw a little spotting. what are the chances of me getting pregnant?

Too soon to know: Conception occurs within day or so of the sex. It takes about 3 weeks for the embryo to make enough HCG for 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.