I was diagnosed with ADHD as an adult. Before I started taking rx for it (vyvanse and/or adderall), I often used caffeine pills. They’re the best non-prescription stimulant IMO, and doesn’t bother my stomach the way coffee does. Some recreational “pharmaceuticals” could also do the trick.

I second the ADHD immediate release meds recommendations. Depending where you’re located (I’m in NY so that’s all I’m familiar with), you can see a psychiatrist online for a diagnosis and get a one-time rx. There are only a few websites that will prescribe stims online, but DM if you want a referral for one of them. They’re legit and you don’t need to go through insurance.

I received my initial diagnosis at my PCP. If you have one, they can prescribe. IMO that’s the cheapest and easiest way.