I have a bad cough. Had xray taken and an on antibiotics for three days. Still terrible. Should I go back to docs or give it more time?

Depends... If you have pneumonia, you likely need more time. If you have bronchitis, you would expect to begin feeling better soon. The cough can continue if there is ongoing airway inflammation which can lead to bronchospasm. Sometimes, bronchodilator and even steroid inhalers may be needed for a short time to resolve the cough. Your doctor can prescribe these medications so see your doc if cough persists.
Yes. If you are still having a cough, you should be reevaluated by your doctor. Sometimes a cough due to a viral illness or bronchitis can last for 7-10 days, but persistent coughing may also be a sign of reactive airways disease ( a form of asthma) and if so a bronchodilator inhaler and/or inhaled steroid is the recommended treatment.