I was diagnosed with ADD (I have the MTHFR gene mutation which causes Autism and symptoms of Autism, ADD being one of them), and the issue you're describing is very similar to what I've experienced really all of my life.
From what I understand (now, I may very well be wrong...) your hearing should be perfectly fine -- are you able to really absorb yourself into music and perhaps even separate different tones/instruments very easily? Musical instruments' tones are processed by a different part of the brain than language, and part of your issue I believe is something as simple as having a weak spot in the area of the brain that processes language, so people's words are all going in, but not all of them make sense.
To go with that, with ADD you normally have to allocate a lot of your brain's bandwidth to one thing at a time, so if it's being used to do whatever you're doing/thinking about, the area that processes language would sort of be idling or dormant, causing you to not hear words you're not paying attention to.
Then again, there are other factors where someone with ADD is more aware of their surroundings, so they pick up little distant sounds or certain ticks in the room. This part kind of confuses me because you can completely ignore someone saying something due to not paying attention to it but still catch on to a click you also weren't paying attention to -- that may simply be a part of the brain's natural defense system, saying, "hey, look over there; that sound may have been from something dangerous," which is a common thinking pattern for someone with low serotonin levels or the MTHFR gene mutation.
Don't quote me on any of this until you've done a bit of research, because this is all stuff I heard from my doctor and therapist, BUT it may have morphed in my head and now be slightly inaccurate.
As for help... I was prescribed with Adderall, and I must say it really does help with actually listening to something someone has to say instead of hearing the first few words and thinking about how funny their voice sounded, then about their vocal cords, then singers, then Adelle, then modern Pop music, then how much money all these artists have, then what kind of cars they have, then how an engine works, then inventions that have changed life as we know it, then "what if we didn't have this?" then--whoops, were they saying something?
Anyway, you could see a doctor and get a prescribed dosage of Adderall, but be careful; it's the most abused drug in the country. A LOT of college students that don't even have ADD take it to give them an "intellectual edge," and many take it more than what's considered healthy for them. Just be careful if you decide to.
Be SURE to see a doctor first and talk about it before just grabbing the medicine, again, IF you decide you want to take it.
I hope this may be of use to you, and good luck. :)