The hammering alone messed up my elbow" - yeah that's real. What helped me was switching to a lighter sledge and focusing on technique instead of just swinging harder. Also did some stretches before starting each day, made a huge difference.
omg dude that's brutal! my back hurts just reading this lol. i did like 150 fence posts last summer and i thought i was gonna die after day one. the hammering alone messed up my elbow for a week. hope you've been taking it easy and treating yourself to some ice packs or something.