Just ask for a higher dosage. Don't worry about feeling lame about it - that's what they're there for, and they won't know that the meds are wearing off and you need a higher dose unless you say so.

I always have had to take ADHD meds in both AM and PM, even with extended release. Whatever my AM dose is, it's worn off by 3:30, so I have to take it again at 2 if I want to keep my head on straight all day.

There's really nothing unusual about this, so let the doc know how it's going for you and they can adjust so you have a combination that's more functional for you.