It might be ulcer but redness and burning sensation could be due to many reasons. You should consult your dentist without any delay.

Can be due to vitamin deficiency..kindly do consultation

It can be ulcer.Mouth ulcer can be anywhere in the mouth.It appear as -a clearly defined margin -yellowish grey area in the centre - red inflamed margin

It could be ulcer or burning mouth syndrome or LP. Needs to show asap

To rule out premalignant.Since how many days?these will provide conditions for symptoms relief

Namaskaram, Your mouth and tongue are lined with a special type of skin (mucosa), which looks (mostly) pink because it is thinner than your other skin (example: on your arms and legs). Some changes to your mouth lining can change its color to white or red.These lesions must be assessed by biopsy (tissue sampling for disease). Obviously, risk factors (biting ,physical or chemical irritants) can and must be minimized wherever possible and proper periodic oral screening exams should be a priority. Keep in mind, the more you know about this class of diseases, the more empowered you will be. Team Shambhala.