How can I improve my concentration ?

seems like iv tried everything sources have told me i'm 21 years, healthy, i take a high potency multivitamin, extra vitamins c, b 12 and E along with acetyl l carnitine, and alpha lipoic acid EVERY FREAKIN DAY and yet i still have attentional problems, i also try and get 30 min of exercise daily. my medications aren't helping much either... i have social anxiety and i take effexor Xr at 225 mg (targeting serotonin and norepenephrine) and seroquel. yet i simply can't focus on a task, it's so annoying, like when i read something i don't read i skim looking for things that seem important but i can't actually focus on the task, i also have a difficult time following conversations at times, sometimes it's hard just to get my thoughts out whenever I have to speak. i do spend a lot of time thinking, ruminating and introspecting, do you think it has something to do with that? am i thinking too much? what's going on? somebody please explain.