I have the same issue. My pup is 17 weeks old and just finished a round of antibiotics for kennel cough. He had both ears down when I got him, eventually put one of them up but it has flopped again. I never made the connection with the antibiotic so thanks for that. I taped it but he wouldn't stay still, it was murder getting the tape off and it came out kind of lopsided. Now I will just leave them alone and let them do what they do. I found some very good vids on YouTube for taping. Let me see if I can find one for you:
Good luck!