To recite Buddha is to communicate with Amitabha. If in doubt, it actually prevents such communication.
Moreover, to read Amitabha is not to cure diseases, but to go to the Elysium, where there is no pain and trouble ~ It is better to read Buddha hard and go to the pure land with illness as the introduction.
Moreover, the effect of each person's chanting is different, even if they are sincere, it is also different. Because the time was up, Amitabha was led to the Elysium. Brother, don't think this is bitter, but it is actually a blessing. There are still some deadlines, or there are other reasons why we must live in this world, so the disease is cured.
Since you want to read Buddha, you should leave everything to Amitabha, and don't plan it yourself. This is chanting Buddha, it will work!
It may sound hard to accept at first, but at the end of my studies, I hope I can get terminally ill, so that I can recite Buddha with peace of mind, without thinking or doing anything, and I can put it down! So have confidence, if you die of illness in Buddha, this is an absolute blessing!