I am having red rashes all over my body. They look like red welts. It started 2 days ago and while it has not increased it also does not seem to be reducing as well. I have red patches on my back, on my thighs, neck, chest, stomach. There is slight pain in my lower vertebrae as well. I have been using cortizone 10 regularly but except for temporary relief ther is no improvement. I used a new shirt 2 days ago, I travelled by plane to another city and have been eating out regularly. Canyou please tell me the probable cause and solution.