Just got started on meds not to long ago.

I'm almost completely new to meds as someone that was diagnosed with ADHD around 4 yrs old. That's a long story but I originally thought I was diagnosed around the 5th grade because I was started on meds around that time but technically I was not. I genuinely don't remember what they gave me around then but all I remember is they doped me up on multiple different new medications around the same time in 5th grade and I realized quickly that it didn't feel right. I wasn't on it for to long because of the affects so maybe my body could have adjusted a lot better but I stopped taking all my pills to avoid that feeling. I pretty much should have been on medications my whole life but refused because of this, but now I'm on 15mg dexmethylph. This is my about second month of taking it, and the first month I was only on 10mg. First month I didn't notice anything different and almost same with this month the only thing different is I feel more quiet. Obviously it's pretty early on this 15mg for me to see any good difference and it will take time to adjust but I was wondering at some point when do I know it's to high?. I understand that a lot of people that take pills like these have a higher dose of like 40mg+ I obviously get that I will need to move up again when needed but that doesn't mean a dose like that will work specifically for me.

I would rather prefer not to feel like a zombie, or high on crack, so I'm just wondering from others that have been prescribed this pill or things like it: what are the warning signs that it's to low and especially to high?

I've also been told by my doctor this pill is somewhat of a take when needed, but someone I know keeps saying I'm throwing myself off because I wake up to late and can't take the pill later in the day so my sleep isn't effected. Even though my doctor has given me false information before I do trust her on this, but I'm also wondering am I wrong for skipping every once in a while?