Asthma reliever inhalers in the USA?

I am currently still using the reliever inhaler I bought back home in South Africa and I am just wondering whether I will need to have a prescription from a doctor in order to buy one here or if they sell it over the counter like in South Africa. If I need a prescription would one from my doctor in South Africa be valid here? I just need it from time to time like when seasons change, its controlled and I currently don't have a doctor here in the states.I know this should be in the health section somewhere but I figured that parents will know the answer this. Thanks in advance.