What Causes Red Lines And Itching On The Legs?

I have these red stretch mark lookin lines that appeared overnight on the inner parts of both my thighs, it may be a rash because it itches. My concern is that I take Pristiq and Lamictal for Bi-polar disorder. The Lamictal I was told can cause a rash that is dangerous, its covers a fairly large part of my inner thighs. I think it might be spreading as well, could this be a rash even though it doesnt quite look like one yet?