Hi.
First of all, orgasm does not affect implantation, whether caused by intercourse or not.
It is a little too early for you to test - 10 days post transfer would be the earliest you'd hope to get a positive - so, yes, you could still get a positive on Monday.
Transferring 3 embryos doesn't significantly increase the chance of pregnancy, so don't kick yourself over that. If this cycle wasn't successful and you can't go ahead with another cycle soon, remember that things change over time and maybe in a few months or a year, things will change.
Good luck with your test on Monday :-)
Rachel Inbar
www.FertilityStories.com