Ulcer on bottom lip causing bottom lip membrane to turn a bit purplish at one spot. why is this?

Be sure of diagnosis: Get examined please. Canker sores are common aphthous ulcers of mouth that occur situationally, often in response to stressors, are bacterial or viral, ; can be treated topically with many otc products that reduce local discomfort ; potentially speed healing. However, oral/dental problems ; a number of systemic diseases cause canker sore-like lesions--crohn's, behcet's, std (sexually transmitted).