Hi Dallas,   It's difficult to give a definitive diagnosis over the Internet, but although Amoxicillin (and other antibiotics) frequently cause allergic reactions with symptoms such as hives, it's usually while you're taking them, not a few days later. So, although I can't be 100% sure, I'd be surprised to learn that your hives arose from taking the Amoxicillin.   The dust storm is definitely a possibility, I suppose. If nothing else, it could certainly be considered an irritant. And there is the chance that the swirling winds that carried the dust into your car were carrying other irritants or allergens, such as pollen, as well.   The best person to answer this question is probably your personal physician. An allergist could do allergy testing if you continue to have problems. But, hopefully, this is a one-time occurrence. Are you under treatment?   To your health, Kathi