Having kind of ulcer looking bump on gum. but no pain. i noticed since 3 days.what it will be ?

Could: be a CANKER sore...(Viral) See your Oral Health Professional for a definite Diagnosis..sometimes anti-viral or Dental treatment is available! Hope this helps Dr Z

Gum bump: It could be lot's of things from a traumatic ulceration to an infection. That's why it should be looked at by a dentist to know for sure. Some lesions of these types do not require treatment, are self limiting and of no concern while others can be serious and require treatment.