Constant DC and lagg - No latency issue and no other internet issues. HELP!!!

Hi,

Everytime I log on League I can play for about 2 - 4 mins and suddenly everytime I cast a spell it won't cast, the champion will still move around the screen sometimes and then I will DC and connect again 10 secs later, I have not changed anything, my internet has been the same speed for years and no other connection issues or DC only when playing league.