I have a lump under the right chin and difficulty swallowing, yawning, speaking. what could this be?

Have it checked out: Your (ENT) doctor should be able to palpate it, and examine your eyes, ears, nose, and throat to determine what it may be. S/he will be able to tell if it's a swollen lymph gland, or a cyst or mass, or related to something else. Without more specifics, it's difficult to determine. If not just an inflamed tonsil, it may need to be imaged by us, and see how much of it is affecting your swallow.