Thanks for using the forum.
Unfortunately, I cannot open your link to see the picture. I know that any sore in the mouth can be very painful. If you have an open sore like an ulcer it can be caused by any trauma to the mouth. Sometimes just bumping with your toothbrush can cause a painful sore that can last several days. . A warm, salt water rinse can provide some pain relief while you are waiting for the ulcer to heal. Rinse a few times a day with warm salted water. It can coat the ulcer and aid in healing. There are also over the counter peroxide rinses that you can try. These are available in most drug stores.
If the lump is not open, or does not appear white if you look at it, and does not clear up in the next couple of days, you might want to have it checked out by a doctor. Sometimes a lump like that can indicate an infection or a blocked saliva duct. If that is the case, a doctor could prescribe the appropriate treatment.
I hope you are feeling better.