Hello, Sinusitis can cause by bacteria or virus infection. Mostly it from allergic rhinitis that can cause nasal swelling and block the mucus from the sinus to flow. So it results in sinusitis. Antibiotic help for sinusitis if it from bacteria. For long term prevention sinusitis, you have to treat your allergy symptom. Like antihistamine drug or nasal spray to open your upper air way. How does your rash look like? Dry or scaling? Fungal rash common appear in the groin area because the wet area and also can be from long term Antibiotic drug. If you have that kind of skin you use an antifungal cream. For allergy, rash should be puffy rash(swelling), pale red bumps patch and welts on the skin that appear suddenly. If you have that kind of rash Benadryl can be helpful. Simple skincare like avoid scrubbing your skin, use little soap as possible, Hydrocortisone cream 1 % may help your rash. But if you have respiratory tract involve like swelling throat difficult to breath please go to see your home doctor as soon as possible. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Heang Chan Raksmey, General & Family Physician