I Got Mad Playing Golf Yesterday

For the first time in my life I got really mad playing golf yesterday. My back has been sore lately, actually since the birth of my second child three weeks ago (is it stress?) so I haven't been playing much golf. My wife gave me the green light to go out yesterday because it was, after all, Father's Day Weekend. I was scraping it around for the first six holes, two over par including two lip-outs. I proceeded to bogey the next five holes in a row thanks in part to little or no power off the tee (the back?) and absolutely no confidence in my swing going into the greens. My chipping was mediocre and I continued to narrowly miss putts. After making par at the easy par-5 12th hole I'd hit a decent tee shot on the 13th. With 150 yards left to the flag and facing a stiffening wind, I decided to try and hit a punch-draw 5-iron from a hanging lie in the rough around a tree. Of course I smothered it low and left into the tree, but still I was left with a little 9-iron to the middle of the green. I hurriedly hit the shot well left of the green and could no longer control my temper. I cussed and slammed my club into one of the legs of my stand bag, bending the leg and breaking the pivot mechanism that makes the legs cast open when the bag is set down at a slight forward angle. I'm embarrassed to admit it but I lost my cool. Just two weeks earlier I had played my best round of the year, a 78 that easily could have been a 75, casually strolling around the course and taking what it gave me all the while, standing over each shot simply thinking "I'm just happy to be here." So why couldn't I keep it going? I need to get mentally tougher, of course, but that's the hardest part of improving at this often diabolical game of golf.