Yeah, that part seemed odd to me too. I feel like it needs a couple of changes to make sense:
(1) It actually includes some means of monitoring arousal and orgasm (like an implant or at least a wearable; it wouldn't have to be on the genitals; even access to the spinal cord would give you sufficient data to recognize an orgasm (then again if it's like a cockring or testicle implant, it could plausibly read his sperm count as well)).
(2) It doesn't know if you're pregnant until a couple of weeks have passed, because you are absolutely right, implantation can take that long.