Pain In The Jaw, Lump At The Bottom Of The Jaw. Concerned

Hi, i am quite worried about this. I have found a lump.. it is on the left side of my face but it is weird!? I noticed it the other day when i had my head down reading a book. I had a really sore as if grinding pain on my jaw. I lifted my head up and then put it down again, (as though making myself have a double chin ) i felt the right side of my face and at the bottom of my jaw is a lump. It is in between my chin and ear and can move around. It disappears when i lift my head up? I ve tried feeling it too attempt seeing where it goes but it just disappears under my face? I am going to see my doctor tomorrow but i need a decent night sleep and this is just scaring me? Hope you can help. Thankyou