implantation bleeding with kids close in age730-9am

Ok I'm not here to get bitched out or the "You know what causes this right" my oldest is 13 months, dr said I conceived my youngest when he was 5 1/2 weeks old. My youngest is 6 weeks old today, and once again my husband and I didn't wait the full 6 weeks to hit the sack again and my dr won't do birth control until that appt my appt is next week. (he pulled out I know that isn't an effective form of birth control but I don't think condoms in the heat of the moment) I noticed some bleeding today 17 days after having sex, I don't think I've had a period but some weird pp bleeding (it started and stopped for 2.5 weeks) and idk if I've ovulated or not but I know I ovulated early after my first son. is it possible this is implantation bleeding even though it's 17 days after having sex? if so when should I test? I didn't find out I was pregnant with #2 until I was 14 weeks along. if I am it definitely wasn't planned!