4 years old girl has oral ulcer and it happens a couple time per month. is there any major concern on it? any medicine could help or improve immunity?

Oral ulcers : The oral ulcers are caused by viruses, needs only supportive treatment, is she enrolled in day care, lf yes, that might be the reason for her recurrent problem , try to change her toothbrush often, take he to her pediatrician to check her & do blood work. Make her eat plenty of fresh fruits, vegitables give her vitamins daily & make her Gargle with a mouthwash, I hope she feels better soon.

Unusual for a child: of that age. See a Pedodontist (children's dental care specialist) or a dentist specializing in Oral Medicine for diagnosis and treatment recommendations.

Pedodontist: Unusual in a child this age. When lesions are present, have patient examined by child dentist - pedodontist.