What Causes Leg Infection After The Knee Replacement?

I recently had a knee replacement and now have an infection in the leg that I had the knee replacement. I have been told that it is a strep infection. THe Dr. has prescribe ampicillin IV every 6 hours. They are planning to send me home with a PICC line to receive the medicine at home. Is there any other drug that could be ordered that could be given less often than every 6 hours? I am 64 years old and overweight. I had Guillian B. several years ago and have some trouble walking and circulation in my legs. email: YYYY@YYYY