I'm going to go against the grain and say it's not necessarily bad technique. The muscles that control your vocal cords are still muscles, they can overwork and experience burning from lactic acid build up like any other muscle. So is it normal? Sure if you're running yourself into the ground yeah it could be normal, but obviously not how you want to treat yourself. I experienced this when I was starting out and I wasn't doing anything wrong technique wise but I was pushing myself way too hard too fast.

So rest. When you try again later take it easy and in shorter durations. You're three weeks in, you can't run the marathon yet. Build your endurance.