Weaning?

We suspect that DS2 is about to go through some big developmental change, and I suspect that it might be weaning. Friday, after an apparently normal, pleasant day, he was quite upset at home in the evening. Usually he likes to nurse when upset. This time he said, "All done nursing." and "I too big!" He has been saying "too big" quite a bit when upset lately, so that one didn't surprise me. "All done nursing" was very clear, however. He refused the breast (at first) but pulled up my shirt, nuzzled, and cried. I told him he could nurse if he wanted to, but he repeate "all done nursing" and cried even harder. It was very sad. I was very frustrated at not being able to comfort him, or even have any idea why he was upset in the first place. After a while he did approach me again and nurse, so he hasn't convinced himself completely that he is "too big." This happened several times over the course of the weekend. It is very puzzling and somewhat disturbing. I do want to let him decided when to wean, but I was hoping that it would not be so tramatic for him.