You're right....sounds cooky to go into the RE after you BD. Icky! But do it, heck that could be your problem and then you do IUI and get pregnant, right!
I woudl think they could just remove some of your CM and then mix it with swimmers donated by DH and then see what happens under the microscope. But I read that you go in. It's so fun being a woman!
I had a postcoital done before I started clomid/IUI, because i had been ttc for 12 months with no luck. I went in for the test 2 hours after BD. Kind of like a papsmear, but they just suck some mucous out of your cervix(sounds gross I know). My RE actually took me with him to do the test. He put it on a slide under a special microscope and looked for any movement or any sperm. Unfortunately there were none!! But he said it was my cervical mucous that was "hostile". it didn't have to do with DH cause his SA is great. So now i know that i wasn't getting pg because no sperm were getting to the egg. I started clomid/IUI, but the RE still tells us to bd the day after IUI incase something gets through. The postcoital wasn't really that bad. hope this helps.