Lip burning can be allergic, but most of the time it isn't, especially when there isn't any visible rash. Adding ulcers to the mix open other possibilities, including herpes, at least in theory. But I can't understand how you can both have ulcers and your statement that "no one sees what am talking about." Either the ulcers are there, in which case people can see them or they're not. If they come and go, you'll need to arrange for a doctor to see you on short notice.
Having said that, I think you have cheilitis (eczema of the lip.) Treatment that works best includes hydrocortisone derivatives (you can start with the over-the-counter strength), plus emollient creams like Aquaphor or Vaseline (neither requires a prescription.)
You may not find a cause, but you can still suppress the symptoms. If you had some contact, sexual or otherwise, which make you particularly anxious, you ought to confront them, because what you describe doesn't sound transmissible in any sense.
Best.
Dr. Rockoff