So my first question for you is what do you think is missing in your life that drives you to keep moving on to new things? It seems like you are trying to fill a hole in your life. My next question is, do you believe that there is a purpose to this life? Do you believe there is a higher being that we will all answer to after this life?
I have to ask these things because I see so many young people these days in your position. My first recommendation would be for you to take a step back and figure out the answers to those questions I asked.
Since most people would find that advice too old fashioned, then consider what your diet is like, how much sleep do you get, and how much exercise do you get each week?
Keeping your diet under control is crucial in keeping ADD symptoms in check. Cut processed foods out completely, if you can, and if you can't, at least minimize them. Add in as many whole grains, fresh fruits and fresh vegetables as possible. Drink a ton of water, and cut out sodas, juices, and pretty much everything that isn't water. Cut out fatty and fried foods. Cut out the white foods (white bread, white rice, potatoes....). Read all of your labels! Avoid artificial dyes like the plague!!
Do your best to get at least 6 hours of sleep each night, but really, 8 is better. Less sleep equals way worse ADD symptoms.
Try to get at least 30 minutes of exercise three days a week.... Do more if you can. Exercise doesn't have to be anything complicated, just a brisk walk outside will do. If you can get out in the sunshine, do it (just don't overdo and get sunburned!). Sunshine is great for treating depression and ADD.
Also, it seems like you are still pretty young (19,21-ish?), and hormones can go nuts from about 18-23ish (really, it can happen at any age, but it's fairly common during those years). You might think about having your hormone levels checked. Hormones can seriously affect ADD symptoms and make them worse.
Hope something here could help!