I saw the Dr like every few days. I didn't get a certificate but I could get one printed. Would I have had to send one at the time? I was in daily contact and they were like that's fine focus on getting better etc. I also attended hospital.
There will likely be stipulations for handing in doctors certificate in your employment contract. If you assumed you did not need to give them one unless they specifically asked, then you assumed wrong. You should get your doctors certificate to them ASAP.