2 days late, started having brownish reddish discharge, is it implantation bleeding? i also took a pregnancy test and it came back negative but unsure of how accurate that is?

Any new or unexplained vaginal discharge should be professionally evaluated (in person). Colored discharge often means infection, and in sexually active persons your age, that usually means an STI, especially gonorrhea or chlamydia. Get seen soon. Good luck.

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.