Always regular cycle. had period oct 15-20 had sex oct 23 25 27. brown spotting noticed oct 31 barely any and today bu slightly heavier implantation?

Implantation does: NOT cause heavy bleeding. Most often there is no bleeding with implantation. When it does occur the amount of blood is miniscule. Take care.

Protected sex?: If you didn't have protected sex, chances of pregnant are high, for which urine pregnancy test would be extremely helpful. For initial negative test, repeat in one week and check with an OB doctor.

Test: The best thing for you to do is to take a pregnancy test after you miss your period. I know it can be anxiety provoking but it is what will give you the most definitive answer.

Ovulation bleeding: The slight bleeding on day 16 of your cycle could have been ovulation bleeding assuming you would have a cycle of 30 days and anticipating your next menstrual period on November 14. having had sex on day 8, 10 and 12 of this cycle is unlikely to result in pregnancy, even assuming that's from may survive for four days.