Disconnecting

I have a problem for this past week i get disconnected at least once in a game. When disconnect happens i need to exit from my client and relog and i usualy get back in game in 2-3 mins cause client isnt opening at first. I even lost lp and got counted as a leaver even if i get back to the game. I know this isnt my internet connection problem i tried testing connection even called my provider, when i play with my brother i get dc he doesnt and we are on the same internet. What is causing this ?