Giving Yoghurt when someone is unwell, like coughing, is not good. That’s a baseless theory. Yoghurt (curd) has got lot of good bacteria and if anything, it may help you recover quickly. It may help you with the good bacteria in your gut (intestine), specially if you are on antibiotics which kill all bacteria in you gut, good and bad.
Again, most infections are viral, so you should not take unnecessary antibiotics unless your doctor feels that you need them. Do not pressurise them to prescribe antibiotics, as they will do more harm than good. They do not work on viruses, which are the cause of most of the common infections.