What Causes Irritation In The Vaginal Lips?

Have redness/irritation of outer vaginal lips, no significant itching of this area or other symptoms that would indicate infection. Noticed this after wearing tight clothing several weeks ago and then having my period and wearing a pad. Area is kept clean--use only "free" products and white, cotton underpants. Would like home remedy to get rid of irritation/redness--very sensitive to chemicals. The redness seems less after periods of inactivity (sleeping) and more after a lot of walking or sitting. Could this be hormonal? Period is about to start in a week again--I am 45, 120 lbs, 5 feet 4 inches tall. Had similar problem once before but don't recall how I treated it. Very annoying.