There are a number of different kinds of antibiotics available. Certain antibiotics are used to treat different illnesses, because specific drugs are able to kill the exact germs or bacteria that cause an illness, such as pneumonia. Antibiotics take different amounts of time to make you feel better, but most start to work within three full days. If you have been taking the antibiotics on time and you don't feel any better after three full days of treatment, you should go to see your doctor.
In some cases, your doctor may need to prescribe a different antibiotic to make you better. It is important to visit your doctor if your antibiotics aren't working - don't just stop taking your medication and hope to get better. To reduce the spread of resistant bacteria, it is important to make decisions about antibiotic treatment with your doctor.