One important thing that's worth noting: Just because you have trouble concentrating doesn't mean you have ADHD. There are a lot of other things that could cause that.
It's amazing how many people are quick to self-diagnose ADHD, but have no problem spending hours on their hobbies or interesting projects. In fact, you'd be hard-pressed to find anyone in the coding community who never has problems concentrating on uninteresting projects.
The term shows 0 results on PubMed, a repository for studies, journals, and other biomedical literature. (Note: If you search for 'hyperfocus' it will give you results for 'hypertonus' because the original term returned no results)
And finally, the Wikipedia article is heavily flagged with 'Original Research' and 'Unverifiable/Biased Information' tags, and is also flagged for not having any real sources or citations.
I know the term 'hyperfocus' has worked its way into pop-psychology lately, but I've never been able to find reliable research supporting the claim. I am a bit wary of how easily it stretches the definition of ADHD to encompass just about every person I've ever worked with. After all, who wouldn't identify with the idea that they can 'hyperfocus' on video games or fun projects, but have difficulty concentrating on difficult or uninteresting work? Very slippery slope here.
1. The DSM only defines mental illness so that it can be diagnosed. For instance, it doesn't say "prescribe drugs x, y, and z for ADHD". If the DSM doesn't include hyperfocus, it doesn't mean it doesn't happen. It just means it isn't a diagnostic criteria.
2. How much research can you find proving that depression makes people sad or that ADHD makes people unable to pay attention? Do chemists do research on how wet water is? Remember, ADHD is one of the most well-known mental disorders out there. Doctors have been treating it with stimulants for over 70 years. If you can't find research on the subject, it doesn't mean that it doesn't exist. It just means that there's not really any new ground to be broken in the area.
That said, hyperfocus is well known among Psychiatrists and Psychologists. It's just like the other symptoms: pathological versions of normal behaviors. A normal person can put down video games long enough to go to school or work. I can't without medication.
Some additional "been there, done that" comments: if you try drugs, give them time to work. If you trying different drugs, give them time to leave your system. Know that some side-effects are temporary, but each person may respond differently. You may need to try a few different drugs.
If you honestly think you have a real cognitive or neurological problem, keep pushing for help and don't give up.
Having ADHD doesn't mean you can't focus, it means you can't control what you're able to focus on. Non ADHD people can make themselves focus on boring things when they have to, ADHD people find this anywhere from extremely difficult to impossible.