Senate Review for Academic Appeal

Without any context or detail no one will be able to advise you.

I failed resits due to extenuating circumstances and I appealed once and they rejected it

I failed resits due to extenuating circumstances and I appealed once and they rejected it

You can’t appeal just because you disagree with the outcome. You either need to present new evidence that was not initially available, or prove the the uni has not followed its procedures. Have you taken guidance from your SU?
It’s also not super clear what your current status is following the first appeal.

Can you give me advice as I got a new GP letter but I’m concerned they may reject it and say I could have got it sooner? Whats ur advice

Again, you haven't explained clearly what the first sanction was (outcome). Have you been asked to leave the course? Repeat a year? Repeat module(s)? Progressing with a condoned pass? We can't give clear advice if we don't know what is going on, or why - you've failed some resits and you've now added that it's related to a health issue but nothing else.
Regardless, yes, one of the things you need to address is why you only have a doctors note now. What were you doing to manage prior to going for help? Does the condition affect your thinking? Has the Doctor noted how long you have been experiencing issues?