have gotten this sore and it starts as a bump and eventually turns into a shallow lesion with a white/yellow top. never crusts over, just starts to heal. sometimes it will wipe off and leave a shallow red lesion that eventually gets white again and lasts about a week. any ideas? i have never had cold sores before
It may not be a cold sore. Mouth ulcers are quite common and often the reason is not known. If this doesnt heal completely in 6 weeks you should see a doctor or dentist. Smoking can cause them or a rough tooth. Look for a mouthwash specifically for mouth ulcers, which may help.
My advice would be to get this checked as it sounds like you have had it for a few weeks and it could be an infection so needs sorting Either see your GP, Dentist but if this is not a possibility the see your local pharmacist Don't wipe the head off it as it needs to dry out to heal
I advise you to go to your nearest GUM clinic or GP and ask for HSV1 and HSV2 swap and IGG blood tests to be sure. You need to confirm if this is Herpes or not. if herpes you will need to disclose to all future intimate partners before kissing them or sharing utencils or having oral sex as you can infect them even when you do not have symptoms. It is against the law to pass on herpes.
hi i probably should have specified timeline-- ive only had it for about 4 days
OK I thought by the way you said it wiped off you had had it longer, I still suggest that you show it to a pharmacist and they will probably advice which ointment to use, it could very well be a cold sore as just because you haven't had one before doesn't mean you can't get one, they are highly contagious so you could have a picked it up from someone else
hi all, here is a better photo in natural light. not sure if it changes any ideas of what it could be but please let me know, could it be a canker sore? -- appreciate it! 
looks like an oral ulcer to me
Canker sores we call mouth ulcers in UK. Thats what it looks like to me. You may have bitten your lip at some time...even in your sleep. If it hasnt healed in 6 weeks see your doctor but I think it will disappear in a few days to a week.