Ok, this is going to sound so stupid, but it has worked for me with my first baby lol
after intercourse, take two pillows and stick them under your hips, or roll over and stick them under your pelvic bone so that your butt is in the air and you're on your stomach. *this is straight after as soon as he pulls out* stay like that for 10-15 mins. This will help gravity pull the sperm further into your utarus.
*this isnt 100% but its something to try.*
also dont get upset if it doesnt work, just keep trying and just relax it also helps to pinpoint around which time you ovulate as well.
Also, the 'doggie style' position works best,