14 days ago my 7 yr old broke out with the rash assoc.with fifths disease, (confirmed cases at school).  The rash ran it's course and about 7 days later the rash was almost gone. Then 2 days ago  she started to break out ALL over her face, back,chest and arms worse than the first breakout.  I called the Dr. he prescribed Cefaclor.  My main concern is this:  when my daughter had just turned 1 year old she was infected with chicken pox.  Within days of the first "Pox" she developed a secondary strep infection, was sent immediatley to hospital and stayed in ICU for three days.  She also has extremley bad reactions to spider bites. It is very common for her to have "the red line" travel through her little body. A few times we rushed to ER where she received shots of antibiotics immediatley. Im not sure if I'm being an over reactive Mother, but I feel that her immune system may be compromised and should I insist that the Dr. do testing on her to find out why she has such extreme reactions.  What type of tests I'm not sure but there must be something.  Can you help please? Thank you for your time.