How am I supposed to feel on medication?

Hi everyone, I was diagnosed with ADHD about a year ago. When I was first diagnosed, I started with Concerta, but I didn’t tolerate it at all (loss of appetite and other side effects), so I stopped it. After that, I switched to Ritalin, but I didn’t really stay consistent with the medication, I only took it for about a month. Then I stopped again because I thought I could manage on my own.
I went back to see my doctor two weeks ago, and I decided I really want to be consistent this time, which is why I restarted treatment.
I’m currently on 20 mg of Ritalin ER, but honestly I don’t really see any improvement in terms of focus, calmness, or anything like that. The only noticeable thing was maybe on the first day, when I felt a tiny bit more focused, but that’s it.
What’s confusing me is that around 1–2 hours after taking it, I start feeling really drowsy. My head feels heavy, my eyes start closing on their own, and I almost feel sleepy. I also get physically very hungry, but mentally I can’t bring myself to eat, if that makes sense.
I saw a lot of recommendations here on Reddit saying to eat protein before taking it, so I’ve been trying to do that since I started. Sometimes I take it with a protein-based breakfast, but I still keep feeling the same way.
So now I’m confused about what I’m actually supposed to expect from this medication and how to tell whether the dose is too low, the dose is too high or if I just don’t tolerate it well.
My doctor told me to stay on 20 mg for 1–2 weeks, then increase to 30 mg, and eventually 40 mg if needed. But I honestly don’t know how I’m supposed to judge whether increasing is the right move when I mostly just feel tired and weird rather than focused.

I’d really appreciate hearing about your experiences or opinions because I’m feeling a bit lost with this.