You need to put out in the open, in front of someone outside the office the problems of this overburdened route, lack of rcas, and poor management techniques. How can you do this? With grievances. The only mistake you made was ever mentioning any type of "ailment". What you should have said instead is that you were too exhausted to continue working more hours, and to do so would have been unsafe due to drowsiness . Legitimate and not considered a "sickness".
Here's how to fix that.
File a grievance for lack of pay/overtime pay for the day/hours worked, management falsely "assigning" leave that you never requested, management's lack of hiring of rcas to help on those excessively long days, causing undue stress and excessively long days to regulars .
You can break these up into 4 separate grievances. Here's how I would word the grievance questions:
1) Did my manager (name) falsify a leave request of which I never asked?
2) Did (name) not correctly pay me for working my route on (date) in which no one else was paid?
3) Did (name) fail to hire/retain rcas in our office causing undue stress to me on severely overburdened days?
4) Did management cause me to become so exhausted on (date) by working me excessively long hours with no assistance, as to cause such tiredness that it caused me to have a migrain and blurred vision?
This will show that you were not "Sick", but overworked, deserved auxiliary assistance, and have a manager that engaged in falsifying documents to blame you for his ineptness in hiring rcas. Please don't give up this fight, as so many carriers do, you are in the right, you just have to be careful to never give a reason for not following an order, or finishing your route except for SAFETY reasons, or in your case over tiredness.