Sloan- If your positive OPK was Saturday night, you could O anywhere from 12-48 hours later is my understanding. So it might be the safe bet to schedule one last session in? BUT that being said, it is looking more and more like I 'O' before the OPK shows a positive LH surge. The LH is just late getting to the 'pee stream.' I had an ovulation confirmation on my OvaCue on Wednesday and even though my OPKs were getting noticeably darker, they were definitely NOT positive until 11 pm Wednesday night after OvaCue already confirmed my O. I asked the OvaCue specialist about it and she said it is not uncommon at all. For some women OPKs detect too late. OPKs work for some people and for others they just don't. Also, OPKs are only showing you 'that moment.' You could have had a positive OPK earlier that day. When OPKs say that women get their surge in the afternoon, they cannot possibly know that. Every woman is different.
So basically... what I am saying is that 'most likely' you did O on Sunday after your positive OPK Saturday night. However, you cannot be 100% sure. If you did, it looks like your bases are covered, but another BD tonight wouldn't necessarily 'hurt.'
Also, I wouldn't worry about DH. Any sperm is better than no sperm at all!
Unless you know he has a sperm issue, it is probably okay. If not, you know not to wear the poor guy out next cycle!