Goodmornings are quite dangerous, specifically to the area in which you just described brother. If you use a high-trap bar-placement, and aren't getting your form right(not saying you're not), you could be at risk for seriouis injury. Good form requires that you should:
1. Place the bar low on the traps. Similar to where a powerlifter would place it during squats, even if you are going light. The lower the bar is placed on the traps--the less distance between the weight, and the area of most spinal stress, which equates to less stress on said area.
2. Make sure when performing the lift, that the first thing to move is your ass. You need to get your ass BACK, and bend at the knees first, so that the weight is distributed & stabilized more over the Hips and legs, than the lower back.
I saw a Thread posted here a day or two ago, where a dude stated that he just got a new PR on Goodmornings. I mean COME ON. This is one exercise where personal records should be limited to reps with proper form, and NOT amounts of weight for strength. I don't know who the dude was who posted that Thread, but he stated that he did like #245 or some shit, which is crazy. I do 95 pounds TOPS, but with proper form, definitely feel them just fine. In my opinion, always go light, and focus on form when doing goodmornings. The low back is simply too vulnerable during this lift, to risk going that heavy.
Anyhow bro, if you followed good form and weren't too crazy with weight amounts, chances are you might have simply strained the area slightly by the sound of it. Hope it isn't anything more serious than that.