This often happens to women after they have had a difficult birth. The muscles down there can stretch or even be damaged. Yes, you should see a doctor, but one of the most important things you can do to fix the problem is the pelvic floor exercises that often get called kegels.
Kegels are usually just clenching your inner muscles in that area for periods of time to strengthen them, like any other muscle.
If you do this often enough, you will eventually tone that area up and may not suffer from this problem anymore.