Came across your question because I too was searching the internet for answers as I have a similar small pea sized lump on my upper inner cheek . This is not a " bite" lump or a "cold sore" as I have seen suggested on other Q & A sites . It may be a Mucocele . Here is a excerpt from another forum where the person who hads one explains it more fully
"It turns out I had a Mucocele, which is a kind of mucous retention cyst, and is apparently quite common, or at least it is to an Oral Surgeon"" So for all of you people out there who are frantic about that lump in your mouth. Donâspam�t get health advice from me. Go see your doctor. But it may just be a Mucocele."
I fully endorse the final advise - no-one knows better than your GP or dentist so hopefully this will put your mind at rest for the meantime - but self diagnosis is for fools in the longer term so GO SEE YOUR DENTIST . Just like I will