Strep B in the throat

lOkay, so I am pretty prone to sinus issues. I have massive tonsils naturally, deviated septum, and a long history of sinus infections. So when i got a little sick over christmas I dodnt think mucch of it, but this time i began suffering an uncommon symptom an itchy mildly sore throat. and then I developed awful coughing that prevented me from sleeping well. && when i woke up the day after christmas my tonsils were so swollen i couldnt talk well or swollow. I went to the doctor immediately. They tested me for strep && mono, and both were negative, so they sent out a throat culture. It came back positive for strep B. Well i was put on several antibiotics, and healed up. Well i just started college && recently my friend came down with strep B as well && more and more of the girls I hang around with are devolping it as well in the throat. So my question is strep B contagious, how is it spread, && i know it is not typically a throat condition, so why do we all have it && should I worry. Also is it possible I am the root to spreading it? Where might I have caught such a rare bacteria in my throat.