How Is Genital Herpes Contracted?

I just tested postive for genital herpes , from a culture / swab test of the bump on my genital. My blood work came back negative. My doctor said that means I have been recentley exposed. My bf and I have been together 8 months. He got blood work done 10 months ago for herpes and tested negative. How is there any way my swab test came back positive and my bloodwork came back negative? I have only been with my boyfriend the last 8 months, and he has only been with me. If i recently contracted it how would i have gotten it ? My bf's doctor said he hasn't had history of any symptoms and doubts he has it. My bf had 2 bumps on his penis. I got a bump on myself the next day then went to the doctor and they said it was herpes after the swab. My bf doctor said his was too dried up for a swab. He got blood work done today and will get his results back monday? If his test results come back on monday negative how on earth would i have gotten this?