Crunches work the upper abdomen, leg raises work the lower abdomen, and side bends work the obliques (also known as love handles). About 15-25 reps each day should be enough. If you can do more than that, try adding weights to your routine. Note that doing crunches will only build muscle underneath your existing belly fat, but will not burn that fat directly.
This happens to me too. It turns out that I have a tight/overstrained hip flexors. My physiotherapist told me that I need to make my hips stronger to be able to bear the stress of the exercise that I put it through. Exercises such as pilates clamshells are one way to do this. Also, using a foam roller to roll out the tight hip muscles really helps.
It’s not just about weight loss. Having great gut health is linked to good health throughout your body. Scientists in this rapidly growing field are finding connections between gut microbes and the  immune system, weight loss, gastrointestinal health, , allergies, asthma, and even cancer. With every study that’s published, scientists become more convinced that having a healthy gut leads to having a healthy body.