CD 1 6/21
CD 9 unprotected sex
CD 14ish expected O (but unknown LP)
CD 15-16 brownish spotting
CD 16 unprotected sex
CD 18 today (7/8) possibly 2-4 DPO, cramping
CD 28 7/18 expected AF
I still think it's too early for implantation spotting (which is really not that common). You could have O'd massively early, it's just not that likely. Some women say they have implantation spotting early than 6 DPO, but I can only imagine that is extremely rare. So you would combine unlikely early O with extremely rare super early implantation and further combine it with not that common implantation spotting. Certainly I don't put it entirely out of the realm of possibility, but I'm saying it's just really really unlikely. Spotting with ovulation is not that common either, but it's one of those things can happen occasionally and isn't a normal thing for you. Cramping can occur for a number of reasons- hormonal fluctuations, ovulation, implantation, PMS, cysts, etc. But all this speculation aside, the unprotected sex you had on CD 9 could catch an egg through about CD 14. Unprotected sex on CD 16 could catch an egg from CD 15-21. So pretty much if you O'd between CD 8 and 21, (which is likely!) you have a chance of being pregnant.
Really it's a waiting game to find out what's happening. If I had to make a guess I'd say you O'd on CD 14 and that you're 4 DPO today. I'd still expect AF in about 10 days and I'd test in a week and again a few days later if it's negative and no AF. I know it's hard to wait and wonder what's going on. It's one of the main reasons that a lot of the women on this site like to chart their temperature and cervical fluid. It takes the mystery out of what's going on. It can tell you when you're fertile, when you ovulated, how long your luteal phase is, when to expect AF, if you're pregnant, and if there is anything of concern happening with your cycle. If you're interested in starting to chart (if you're not pregnant now of course!) I recommend reading Taking Charge of Your Fertility. It's really an amazing book that teaches you so much about your body. If you aren't pregnant and really don't want to be any time soon I would highly recommend a different method of birth control than withdrawal.