Do you have a older (original when you first started) student pilot cert/medical certificate w/ the endorsements on it? And are you now getting another physical because the first one (Student Pilot Cert/Medical) has expired (medical portion)? If you still have the first one (student pilot cert) you need to carry that with you along with the new physical certificate.
THIS. Because I was the worlds longest time student pilot, I was in the situation, right through my checkride.
You carry two certificates. The first one is your original student certificate that happens to have an expired medical on the back of it. The second one is your current medical.
I can't tell you how many CFIs and the DPE I had who says my two pieces of paper and explained exactly what I said above, which I already knew, "THIS ONE is...and THIS ONE is..." Thanks.