LOL, when we first started TTC I wondered the same thing but was too embarassed to ask anyone!

I eventually found out that its normal! My Doctor said the best thing to do was to have a shower, brush your teeth, go to the loo etc, then go to bed, have sex and don't move! From last cycle I started laying still for 20mins, this month (well, this cycle, last month) i've gone to sleep afterwards to keep as much up there as I can - hope it works!!!