Just a side note, its much more difficult to get the 3 lbw red's when you have low confidence. Its almost impossible to inswing a yorker without going down leg if your bowler has red confidence, but when its green, you can throw a "standard" delivery and it'll go dead straight onto middle stump.
Other than that, as
@tarrantino said, make sure you actually appeal: (batsmen don't automatically walk when edged or hit lbw, don't overdo the appeals though, otherwise the umpires wont give you a wicket on anything other than edges)
If you feel particularly hard done by and playing in a format with no reviews, you can always go to the pause menu, under "Match Review", select "Big Eye". This is basically what DRS would provide and you can see if the ball bounced over (number 1 issue with not being given lbw, which is fine, only shorter bowlers or a really well worn ball will hit the stumps on a good length with any consistency)
Then you know you have a biased umpire!