Cramping accompanied by very light bleeding ranging from brownish pinkish to dark brown 11 days after sex, 10 days from period. Is this implantation?

See your doctor. Bleeding after sex could be lots of things: infection, std, pregnancy, other gyn problems. Implantation bleeding generally occurs at the time of expected menstrual period. Do a home pregnancy test, but best to check it out.
Could be. Check a pregnancy test to see if it is positive. Some can tell you that you're pregnant almost a week before your first missed period.