2 STD tests, Herpes, an 1 committed relationship.?

Me and my boyfriend have been together since April 3rd, 2010. I got an STD test at the end of June- beginning of July. An had chlamydia. We both got treated. It is now over a year, and we have been faithful only to each other. We both have had sexual partners before each other. I am the only one experiencing issues in my lower region. Have had a creamy white, kinda between thick an runny discharge, no smell. My urine does not burn but has had a very disgusting odor the last few months. I occasionally ( once or twice in the first 8 months me an my bf been together) have 1 or 2 blister like things. Usually only looks an feels like an infected hair. It never pops or oozes fluids. An never scabs until a few days before completely disappearing. Haven't had a blister thing in over 4 an a half months I think. I just got my results back from my 2nd STD test an they say I Have Herpes 2. my question is, how in the heck is it possible I have herpes now but not during my first testing??? Please help me, I'm rackin my brain tryin so hard to figure dis out :(