This definitely looks like a mouth ulcer to me. I get them inside my cheeks and on my tongue mainly, and occasionally on the roof of my mouth. What I do is rinse my mouth out with a very mild solution of warm salt water. Not too much salt as this miht make you sick, and also don't swallow it. You can buy OTC remedies for this type of thing, but I do find the home remedy eases the pain and keeps the mouth area very clean too. Oral hygiene is paramount when we have lupus.
Even stress or taking the pill can cause us to have this problem. Avoiding citrus fruits or sharp foods like potato chips or anything like that will help them to heal if they are ulcers. Any mouth ulcer or that type of thing that lasts for more than 10 days should be looked at by your dentist or doctor.