Whether you need a GP note for every time depends on the uni policy on ecfs, but most of them (if they insist on evidence), will accept a variety (perhaps including personal tutor's comment, which can effectively replace GP note).
At the end of the day you have a fluctuating condition/disability (the important bit), so a GP note each time doesn't make sense, particularly for preplanned extensions...(and they should be preplanned - after all, you can always hand work in early, and they should be making adjustments for your disability).
Maybe point out that you are aware that everything landing at the same time can cause issues (can happen with extensions), and that due to past degree you know that you (as with any student) need to plan your time to avoid this. If you've done Gantt charts, you might find it helpful to map everything out and make sure that you don't have work for 5 modules going on during placement (basic one in Excel with months across the top, and modules/placement segments down hte side). This also shows hem that you've thought
, and backs up what you're saying if there are bottlenecks.
This also might help with working out whether what they propose may work for you - which is the important bit.
Flares may change things...but I've known people training in various allied/nursing professions with everything from ME to colitis flares/relapses who have had to work round them - in this case, medical notes may be needed if you go beyond the self-certifying period/if required for assessment purposes if that's what your uni uses, but equally they shouldn't discriminate if you miss some time because of your disability...i.e. you should have chance to make up the hours, although it lengthens the degree (most professions have x hours placement as part of their standards - yours may/may not).
Have you seen Occ Health? I had to see them prior to starting my course, and whilst their usefulness varies, they can be useful in terms of backing up/recommending placement adjustments in letter form...including appropriate lunch break and shift timing (because they can help with placement adjustments/safety).
If this was a private conversation, I'd be asking what support your uni offers students on placement - this varies wildly, but if you have an academic contact during placement time, this should be someone who is willing and able to provide this support, including helping you explain/negotiate reasonable adjustments with your placement (you should be involved in this). This also feeds into the disclosure side - I disclosed my disability to placement providers as required, but tended to frame it within 'If I do z to achieve y, it works out the same as doing x to achieve y' (alternative ways of meeting standards), or linking my limitations to my future scope of practice. I also used to explain that I used taxis so they knew my transport wasn't completely under my control...(but my profession works on one supervisor, one student, so it may be different).
Irrespective of how you feel at the moment, I would want to see plans/support for getting you through year 3...talking to you about the diploma at this stage does not sound awfully positive - this should occur only after you have failed 2nd year twice unless you ask about it (because if they haven't been supportive of dis needs up til now/your condition/support needs have changed, this should be reason enough for you to resit a year as a first sitting).
Sorry, I know that's a bit long, varied and may not apply...but I hope it does work out for you