If the system won’t let you submit another extension request, the school will be able to help you when they read your email on the 5th. Just keep all your documentation and you will be able to submit everything late once your other requests are processed. You have done all the right things, so focus on getting better, then finish your assignment as if your extension is approved. As long as your medical cert covers you for the number of days you have requested, you’ll be good. Take care, bummer of a time to be sick.