Why don't you start a diary since you've joined this site.. diaries help us help you by providing as much information as possible to us...
"Burn" is never caused by overwatering.. yellow tips are indicative of a number of things - nute burn, the beginning of a deficiency, etc... hard to tell from just two pictures what is going on here. I'm not much liking the really dark veins in the second photo... and think you DO have a problem - but we need to see more information. So start a diary with as many weeks of the grow as you can reconstruct and come back with your question....
Good luck...