I have suddenly developed a red itchy rash on my abdomen and hours ago i experienced a similar itch with redness in my front right shoulder area.

Itchy rash: This itchy rash may be an allergic reaction to something external like clothing,detergents,cosmetics or something internal like medications,foods. I assume insect bites or poison ivy,etc are not the cause. Try taking an antihistamine by mouth and apply corticosteroid ointment. If no improvement or more involvement, see your physician for evaluation and advice.