Prescription of an antibiotic by a doctor will be the outcome of weighing the possible good effect it impart and possible side effects. That is, an antibiotic will be prescribed only if needed. In case of dental or gum infections antibiotics may be prescribed after proper oral examination.
If the conditions like bleeding gums need a dental prophylaxis or cleaning, it should be done without fail. That will remove the cause of infection that induced bleeding. In such cases taking antibiotics alone won't solve your problems. The approach should be to remove the cause or factor that caused the disease. These all will be done and approached properly by a good doctor.
So consult a doctor before taking antibiotics. Don't neglect the bleeding just because you feel like it's not affecting your overall health. A localised problem like gum bleeding can cause generalised health issues if neglected or if it is not taken care at the beginning.