I have a rash on my neck, it was scaly at first but now it's smooth and red. i have been quite stressed, it's occasionally itchy and have had for about three monthsi did accidentally rip off a skin tag that was there from itching then the rash from?

The fancy name is neurodermatitis, which comes when you focus on an area and touch or scratch it repeatedly. Over time the skin thickens and itches more, changing skin tone. The lay term is worry rash. Quit scratching and it is likely to fade in time. Your doc can confirm the label.

I am very reluctant to label nonspecific rashes like this without actually seeing them. Neurodermatitis is a possibility, as the previous answerer said, but there are a dozen other possibilities. See a dermatologist and get a definitive diagnosis and treatment.