Are you diagnosed? I understand that you can ask for accommodations with a diagnosis and it will be much trickier for them to fire you (if the reason is ADHD related) but I know that can take a while.
There are things you can do to manage it and help even without a diagnosis/medication. I am medicated now but I did have 7 years unmedicated after initial diagnosis. If you are undiagnosed into adulthood too you'll likely have lots of unhelpful coping mechanisms which can cause problems of their own.
In conversations with customers - do you have the option to slow it right down and take notes as you talk? This helps me a lot.
With ADHD, working memory capacity is affected - it's not that you aren't paying attention to what people are saying/instructions at school etc, it's more like your mental "scratch pad" is smaller than other people's. Our ability to hold things in mind while we work on them is very compromised, so it helps a lot to get information out of your head and onto something external. With everyone's working memory (ADHD or not) if you try to keep too much in there, it sort of gets "shoved off the other end" and disappears into the ether. I think ADHDers have a double whammy of having a smaller working memory capacity, but also trying to shove too much on there often because we tend to lose things like notepads, lists etc so it feels "safer" to keep it in mind but it's very much not!
Hormones can affect it in women too so they call it the four Ps - puberty, progesterone, pregnancy, perimenopause. ADHD can worsen at all three of these times of life and the progesterone part is about the menstrual cycle - many women find that their ADHD symptoms are worse in the week before their period.