May i make a suggestion? If you are just standing there, it wont work. You must move around alot and run around. A pokemon with the Ability Flame Body Being in your pary wont harm the egg, just make it hatch faster. (You still need to move around).
If this is not working, consider looking at your PC boxes. If they are full, you will need to release a few Pokemon so that there will be room in your party or PC boxes.
All Pokemon Species hatch at different speeds. So, if you have taken up breeding a NEW pokemon that you are not as familiar with, perhaps you'd better take a while to hatch this egg. Maybe do a bit of Research on this Pokemon, as a Proffesor would.
If these dont work, i reccomend you look up your requested information.