Can I know what infection did your physician told you have.
Having antibiotic on an empty stomach causes lethargy and weakness especially if one is underweight/anemic/underlying other disease.
If you have acidity issue, taking an antacid (omez 20 mg 30 minutes before breakfast once a day) is really helpful.
It is usually advised when patient is put on antibiotic course
Next Steps
visit your dentist back always when you tend have issue with any of the medicine you have been put on
Health Tips
drink lots of fluids, have medicine only after food.
if not feeling hungry, try to have small snacking in between meals as you require antibiotic and energy to fight infection