Hottopic, I wanted to ask you if you base your scalp really well. The night before a relaxer, if you coat your scalp with evoo and cover with a silk scarf (no plastic caps because you may perspire) that really helps. A lot of people say that petroleum jelly is also a good protector. But I've got to tell you that if you are burning, be very careful and take it as a warning sign. Most of my head never burns but the back always has on occasion. The last time I relaxed the back of my hair (just before Thanksgiving) I coated my scalp, especially in the back, really well, and it did not matter. The minute I put the relaxer on the back of my head it felt like it was on fire. I later tried a no-lye on that hair and even though it did not burn at all, it also would not relax or straighten at all.
My point is that with good basing and good application I do not think it is normal for your scalp to be burning. Your scalp is telling you something, maybe you've developed an allergy to lye, maybe your scalp is extra sensitive, maybe the relaxer is too strong. I don't really know the answer to your question. But I thought it might help to hear someone else's story. I am now in a dilemma because 75% of my hair loves lye and 25% burns like ****. In the end, I may have to use no-lye or nothing on that back portion of my hair. From here on I'm going to try to listen to what my hair tells me before it has to scream, "Don't do that to me!"
Good luck.