I took a pregnancy test 13 days after i had sex and it came back negative, but now my breasts have been sore for about 3 days now. was it too soon to take the test, could it be wrong?

Tested too soon: Test should be done at least three weeks after sex. Conception, as defined by the generation of a fertilized ovum, occurs within day or so of the sex. However, it takes about two 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.