What Causes Short-lived, Itchy White Welts Appearing At Night?

I am experiencing short-lived itchy white welts only late at night, never during the day. they are not round, but long, thin, white and raised. they seem to last for less than an hour, no more than half an hour.i have looked up information about hives but all of the info describes them as being round and red. I can't imagine what this is but am concerned it has something to do with my liver. I simply can not find any information online about thin, raised, itchy white welts of various lengths. Its been happening for about a week, once a day, always late at night, although one of those days it didn't occur at all, and when they do occur they vary in degree, intensity and number.What is this?