How did you end up getting your medicals done so early? They are good for 6 months, and people go for medicals after approval and when they have an interview date already. You should have gotten medicals about three to four weeks before your interview. All that aside, the embassy will require you to get another medical exam, so no need to worry about your visa expiring. Sometimes people wait a while before they travel to the us and those are the ones that have to be concerned with expiring medicals. Also, people who are put on ap, they will always have to get another medical exam before their visa is issued. It could be that the consulate and nvc noticed your medicals would expire before you travel and will be alerting you to get another medical exam before they issue your visa. But this is just speculation. I hope this helped.