Re: how long after conception does spotting normally occur?
Becoming sexually active, either for the first time, or after a long period of abstinence, can effect your period. You can spot, you can have a heavier period, it can be late, or early, etc etc.
Implantation bleeding/spotting usually occurs around the same time as your regular period. If you continue spot and nothing happens, I would test. If it's negative you can either make a doctors appointment for a blood test, or re-test in a week.