Yup, as others have stated, I'd tell the doctor that your sister has been diagnosed with ADHD and that your symptoms are very similar. I'd also talk about your experiences with previous meds. It's entirely possible to have multiple things going on, so I think having an honest conversation with the p-doc is the best way to go.

I think most medical professionals are a bit turned off by patients that come in and say "I've decided I have xyz and I want med abc to treat it." But, if it's approached in an exploratory way, where you're having a conversations about symptoms, family history, and what has and hasn't worked in the past, you're likely to see a much more receptive response.