Believe it or not, this is usually not as much of a thing to worry about as you might think, though it's almost always a big newbie concern. Thanks to variations of fashion there are a number of ways to deal with a pelvic bulge. For instance, with something like a pleated skirt, you can often get by fine just leaving things loose. In fact, even with a smoother front skirt it's possible to wear something to flatten the front enough not to bulge.
I suspect that your tucking problems are due to both inexperience and, perhaps the design of undies you're wearing. There are some things (such as thong unders) I find quite impractical, though some may manage with them. I find a more full cut control panty can be quite comfortable and, for me at least, holds a pretty comfortable tuck. I've also had luck with Hanes girls' yoga shorts, ordered in a size to be fairly snug. I've bought them for as little as $4-$5, too.
Another thing to consider is that most people are not watching your crotch. While you want to take some effort to keep things out of the way down there, pay attention your overall look. For instance, beard cover is way more important than crotch bulge.
