Your clinic should give you advice about how to manage intercurrent infection.  If you are not sure that you are unwell enough to need to take antibiotics, they may not be needed and you could wait until Monday.  If it is a definite bacterial infection, then you should start antibiotics, following the guidance given to you by the prescriber and then let the clinic know as soon as you can (e.g. after the weekend).  Lots of clinics would like you to provide a sputum sample for analysis just before you start antibiotics if possible and may have provided you with sputum pots for that purpose.