Some doctors prescribe antibiotics because their patients expect it. Or else he suspects a bacterial infection of some kind. Next time, ask him why. If you have started, no harm in finishing it. The antibiotics should knock out any bacterial infections that may be taking advantage of your weakened state.
Because of my high blood pressure, there are few medications I can use. I end up falling back on natural remedies to carry me through. If you are this sick, GETS LOTS OF REST. Eat well. If you are nauseous, start with clear liquids and work your way up to solid foods. Eat/drink frequently, eat/sip small. For coughs, tea with honey. The warm vapours should soothe your irritated passageways as well.
1. Clear liquids - water, pedialite, gatorade, tea, beef or chicken bullion
2. Simple carbohydrates, like dry toast, dry soda crackers
3. chicken soup, milk, hot chocolate (for comfort)
If you hold down the above, you are ready to eat normally again.