Iam 26 years old , from 3 years ago ,I was take 2 shots of Hepatitis vaccine e out analysis ,then after 2 months of 2nd shot , do analysis for HBsAg and was +ve and take 3rd shot of vaccine and after 3 months of 3rd shot , the HBsAg was -ve , and make this analysis every 6 month eor 2 years , and suddenly found HBsAg +ve . what I do ? and what the medical explaination eor appearing and disappearing HBsAg ?