I just bought my chicks last sat. During the next day I noticed quite a few of them panting, despite the availability of fresh water. There were also cooler parts of the box they could have laid in but continued to lay huddled under the warmer spots. I was quite worried but also quite nervous still about the heat lamp as I wasn't use to it. We work and go to school for the better half of the day so I didn't want to move it from the secure spot I had it in. I also didn't want my chicks to get cold if I shut it off for a bit as I had just got them. I let it go for a little bit to see if it subsided and I never seen another problem other than that one day, even though they are bigger and more active, not to mention the lamp has never been raised or shut off once.
I'm not sure, but I think my lamp was hotter in the first 24-36 hours of use. If the problem persists I would probably move it up, or just make sure there are cooler areas for them that aren't really affected by the light. If it's more than they can handle they should hide behind something or lay in a cooler corner on their own, from what I've gathered anyways..
As far as the yawning, I can't really say but have questions also..lol. My gold sebright was doing something similar just this morning. I've never seen her do it before. I was holding her and every time she would start to fall asleep & wake back up she would do it. At first I thought this was yawning, but then she started doing it every 20-30 seconds and I realized it didn't really look like yawning. It honestly looked like an imitation of crowing without sound. It would open it's mouth really wide as if calling and stretch it's neck up when doing it. I've had suspicions of this one being a cockerel, so I'm wondering if despite the young age this could be an early indication. It's all I could make out of the odd action. lol.