Don't say anything about the drugging, just ask your boyfriend if you've been having sex at night and don't remember because you're leaking cum.

Don't let him know you think he's drugging you, based on how he reacts you should be able to tell if he's drugging you, if you're talking in your sleep and seemingly awake at times with this new medication, or if he's just straight up having sex with your unconscious body when your medication kicks in.

His reaction will be very defensive if he's drugging you and probably total denial, if you seem to be awake when he's doing it he'll probably be surprised you don't remember and a little embarrassed and want to talk about it, if he's having sex with your unconscious body he'll probably admit to it after potentially a little denial and then start justifying and asking if you're okay with it, not sure you'd count that as rape? Just don't tell him you think he's drugging you.