Lower ab region sticking out is a very common problem -- even among "skinny" people. As some people here have been hinting at, the problem is usually anterior pelvic tilt. Basically, this means your pelvis (hip bone) is tilted forward. For evidence of this, stand in front of a mirror and tilt your pelvis to a neutral or posterior position and watch your "lower ab bulge" almost disappear.
This is especially common among women, because of high heels, sedentary lifestyles, and also just because a "feminine" way to walk is with an anterior pelvic tilt. Men have a problem with this because of tight hip flexors (sedentary lifestyle and/or training imbalances).
Problem is, people often think their "lower ab region" sticks out because they need to do more "lower ab" work, so they do a bunch of leg raises and stuff, which often just makes the problem worse. Leg raises, if not done properly, work the hip flexors a lot (even if done properly, they will still work the hip flexors a little). This leads to tighter hip flexors which just makes the problem worse.
The floor bridge exercise (looks like you're trying to hump the ceiling) is good to teach your body how to activate your glutes. Tight hip flexors means lengthened glute muscles and reciprical inhibition of glutes (too much hip flexor strength/activation, too little glute strength/activation). The floor bridge teaches you how to activate your glutes (learning proper motor patterns). However, this exercise itself will not fix the problem, it is just a first step. You will not get a lot stronger glutes by doing this, it will just teach your body how to activate them.
In short, the long-term solution is to stretch the hip flexors regularly and to strengthen the glutes. Core work will help, too. You might want to consider ART (Active Release) on your hip flexors, because you can stretch and stretch those hip flexors all you want, but if you have any adhesions, scar tissue, or flat-out shortness of the muscle, you need to have it worked on to restore the full length of the musculature.
Another good exercise to help with glute and core activation is the "bird-dog" -- get down on your hands and knees, arms and femur perpendicular to the ground. Then extend one arm and the opposite leg straight out, while keeping the rest of the body in the same position (no leaning to one side). While doing this, tighten your core and your glute muscle on the same side as your extended leg to maintain position. Hold the position for 5-10 seconds, then repeat on the other side. Work up to 3 sets of 10 or more.