2 days ago I noticed a lump under my chin underneath the skin. I woke up this morning & it got bigger. Could you tell me what it is What should I do?

Lump. It may possibly be a cystic lesion perhaps from an ingrown hair? If it becomes red or inflamed, it may require antibiotics. Some cysts spontaneously resolve. However, if lump is not resolving over the next few days or worsens, you should visit your doctor for further evaluation to rule out a more serious condition.
Could be several ... A couple of things could be going on. It could be a "submental" lymph node related to some sort of issue with your lips or tongue. It could be a skin cyst or fatty mass. In the end, there are just guesses and the only way to be sure is to be seen in person. I would recommend this as it allows appropriate treatments and follow up to be set up for you. Best of luck. .