They may ask you the nature of the prescriptions and who they are for. You are not allowed to bring any medicines into the U.S. that are not for your own personal consumption. This includes both controlled and uncontrolled medicines. It is a misdemeanor to fail to declare all medicines when asked to do so. Only drug smugglers have to worry when they declare their medicines.
Most antibiotics are about half the cost of their U.S. counterparts.
It is quite common to save a thousand dollars for six month's worth of drugs, if your total bill normally exceeds two thousand dollars. You will see quite a number of fellow Americans waiting in line to buy their prescriptions too. It is not a scary or spooky adventure.