I had a tiny bump of the bone behind the ear. right ear. it painss little when touch. around if it there is redness and tenderness. all other thing is fine so far. i am not sure is it a mastoid or something else. 24 yrs old male. 2 days problem?

Cyst, insect bite, pimple, etc. The possibilities are legion. If bump does not completely disappear in 2 weeks, or if it at any time worsens compared to its current status, see you GP or Urgent Care.

You could watch and wait. If the bump more than doubles on size, becomes ulcerated, bleeds, other bumps, appear, you get fever or lose weight, see a doctor.