What Causes Cold With Residual Cough And Fever?

my sister isnt well at the moment it started last week when she develop a cold which she got rid of and it left her with a cough but now her temperature keeps going up and down my mum is giving her paracetamol and it seems to be working shes 14 years old and i was wonderin if you could maybe help me with what it is she might have thnks c