It's possible they think it is pertussis (whooping cough), which is going around quite a bit in our area in the Pacific Northwest--ask your doc if that is the reason they gave it to you. The problem is that the symptoms could be almost anything at first. It could be just a cold. It could be an allergy. Neither of those would be helped by antibiotics. But if pertussis is going around your area, they may be simply giving out z-packs (the antibiotic of choice for this) prophylactically, since you can greatly reduce the level of illness you experience if you catch it early. The only way to tell is to do a culture. And that takes 2-4 days to come back. It would be fine to ask them to do one and wait until the culture is complete before starting antibiotics. Unless you know you have been exposed to pertussis, it's probably a good idea to do that before starting on that very strong antibiotic. Just a few weeks ago, my daughter was exposed by her friend. Her friend had similar symptoms to what you described and her mother thought it was just a cold. She waited about a week or so, but after it didn't get better THEN she had her tested. Another several days later, they confirmed pertussis. By that time, the symptoms were more difficult to deal with, but still not terrible. My daughter started having the same symptoms about then, so we got her tested right away, and did put her on z-pack prophylactically. She turned out to be positive. She was almost completely feeling better within a couple of days. Then my partner started having the same symptoms. He chose to get tested, but not start z-pack right away--and his test came back negative. So it's hard to know. I think the key is to get tested soon and then wait until you know the results--shouldn't get too much worse in that time, unless you are already really miserable.
Either way, the things to do at home to improve your immune system's ability to keep the illness down and help you recover more quickly are the same:
-LOTS of water, tea, and other healthful fluids. Among other things, it helps keep all the tissues moist and breaks up mucous, as well as keeping all your cells functioning at top levels.
-Garlic. Raw is best if you can stand it. Or try this midwives' trick--peel a clove and stick in under the sole of your foot inside your shoe. The bottoms of the feet can absorb the constituents--you will be amazed that your breath starts to smell garlick-y. It works! Cooking in any form will reduce it's effectiveness, but if your going to do it, baked garlic spread on olive oiled crusty bread is yum!
-Echinacea. Best to get tincture form--the tiny amount of alcohol will not harm your pregnancy, but if you are concerned you can drop it in hot tea and the alcohol will evaporate. Don't boil the tincture in the water, just drop it in the cup after you have made the tea. This is an excellent support for building more white blood cells and making them function better--proven scientifically in a study that was actually trying to prove the opposite because the drug companies were hoping to sell you expensive drugs instead.
-Grapefruit seed extract--An unbelievably effective natural antibiotic, antiviral, antifungal. Brand name is Nutribiotic. 15 drops twice a day mixed in a shot glass of citrus juice. It's a heavy oil that sinks to the bottom, and if you've ever bitten into a grapefruit seed you get an idea of how bitter it is. citrus flavor like lemonade or orange juice cuts that. It will make you feel better FAST!
Hope you feel better.