So, a quick note that I didn’t see properly answered, you being resistant is not the problem, but the bug currently attacking your system. Kind of depends on how you define ‘you’, since it will probably continue to kill beneficial bacteria in your system which are quite important to your healthy existence, but your human cells are already mostly resistant, while it’s called an ‘antibiotic’, it’s better described as an antibacterial, it just kills bacteria (to get very specific, it’s a bacteriolytic antibiotic, but same thing. Very very specifically, it attacks bacterial cell walls, which you do not have). As long as you have killed said bug, you could keep taking the drug forever and it wouldn’t really make a difference. Well, probably wouldn’t be great since you’d become a superbug incubator and it would kill off your good bacteria, but the effects on your human cells would be negligible.
So, if you get a new infection in the future, a truly new infection that wasn’t just lying dormant (which is the case for most things you’d take Amoxicillin for), it doesn’t matter that you’ve taken Amoxicillin before; this new infection is new, and if it’s resistant to the drug it will have been because of a different source making it resistant and whether you have taken it or not before is immaterial.
Now, if you stop it now and your illness isn’t dead, that will indeed lead to resistance, but that’s just the same illness evolving, it’s not a new infection, and that’s what leads to you passing the newly resistant bug to more people. But it’s different then being able to ‘use it later’. And it won’t take long to come back, either. However, your doctor should understand that, so if you trust his judgement you should be okay with changing things as he directed. Either way, any new infection that occurs down the line will still be affected by Amoxicillin regardless of what you do with this infection.