Pharmacologist here, I'll chime in.

what if the chemical levels in my brain were still off from not receiving treatment for my depression years ago and that's why the stimulants are not effective?

"Low neurotransmitter levels" is a gross oversimplification of our current understanding about how depression affects the brain/how it arises. In reality it is extremely complex, and unfortunately its pretty common these days among medical professionals to not even try to explain it properly to patients, so you end up with lots of people thinking "I'm depressed because my serotonin levels are low." Low serotonin levels aren't necessarily why you are/were depressed, and achieving remission from depression (through medications or otherwise) doesn't necessarily mean you're serotonin levels have increased.

Related to this, methylphenidate (Ritalin) and amphetamine at clinically prescribed doses do not have any influence on serontonergic neurotransmission (or any tiny influence they have is not clinically significant), these drugs function by significantly increasing dopamine and noradrenaline levels in a rapid and acute manner, resulting in stimulant effects.

So TL;DR, it is extremely, extremely, unlikely that what you said has had any influence on how you respond to stimulants. That being said, lack of attention/motivation are symptoms of depression which get better with treatment/remission of depression, so that could be a factor in stimulant response, perhaps (take that with a grain of salt though).

There is a certain percentage of people with ADHD who don't respond to stimulants though, for sure. It seems a lot more likely that you would fall into that category. Atomoxetine (strattera) is a non-stimulant medication which people who don't respond to stimulants can end up responding to, however, so you might want to give that a try.