There is no requirement for a GP to provide a sick note for periods of incapacity lasting of less than 7 days or less or the first 7 days of longer spells.
A Med 3 (white) is a sick note, which can be issued to a patient when seen the same day (or the following day). It can be given to return on a specific date – referred to as closed (but not more than 2 weeks from the date of signing) or for an open period e.g. 3 weeks.
A Med 5 (pink) can be issued under the same terms but is usually required when the period of cover starts prior to be seeing seen or when the doctor has not seen the patient in person (but has documentary proof that they are unwell, e.g. a discharge letter from hospital).
For periods of illness preventing you attending lectures, less than 7 days you do NOT need a note.
For illness preventing you completing course work/assignments you can only be given a note if unwell for more than 7 days.
If illness prevents you attending and assessed practical or exam you must attend the doctors at that time and be certified as unfit to attend.
If you have any questions regards to extenuating circumstances please see the university guide. https://www.nottingham.ac.uk/studentservices/services/extenuating-circumstances.aspx