You don't actually have to do this. When the male ejaculates inside of you, the sperm is placed immediately where it needs to be. However, some women think this helps, and the general recommendation is 15-30 minutes. If you've not gotten pregnant after almost 2 years though, it would be better for you to see a doctor and make sure you have no underlying health issues in either you or your partner.
I always held my legs up and put pillows under me for 5 minuted the most then i would go wipe just a little. I was told do not wash or pee for you will be wiping away or peeing out the sperm. It took me 5 months to get pregnant i am now recently 22 weeks pregnant.
Everyone says that you are supposed to lay on your back for about thirty minutes. If you have been trying for over a year now you may want to see a fertility doctor to get some answers