Likely not a problem with weight, you were riding on loose spokes for a while which stresses them right at the bend.  After a while they break. 

When you tensioned and trued them before, did you remember to release them?

When you tighten a spoke, it tends to twist resulting in stored torsion that will eventually be released resulting in a loose spoke.  An experienced wheel builder will release this torsion while trueing the wheel by squeezing parallel pairs of spokes.  See here for a complete discussion.

Edit to add:  if you rebuild the wheel, be sure to replace all the spokes.  The remaining ones are likely to be fatigued as well and will probably break in the not too distant future.

My opinion is that feeling for tension by hand is not good for anything unless you are a master wheelbuilder with thousands of wheels under your belt.  So, from this armchair, I'd say your wheels were not tensioned properly.

Something not discussed yet is that one cause of premature wear leading to spoke breakage is failure to stress relieve a wheel.  This may have been the case with your previous/initial wheelbuild leading to worn spokes.  When a spoke is tensioned it develops a conflict between its existing material structure and the stress of being held in position, which leads to metal fatigue.  Stress relieving takes a spoke past its yield point so that when it "springs" back to its static position, it is no longer under stress.  When I build a wheel I do at least three rounds of stress relieving.  You do this by squeezing parallel sets of spokes.  The squeezing action is quite severe: you won't be able to handle the pain in your hands if you attempt this without wearing gloves.