Typically isolated hives, that is painful, itchy swollen, burn, then bruise afterwards. normally on my forearms but now my neck and under my chin.

See a dermatologist: Dermographism? Other diagnosis? I can tell you have not been to a skin specialist because Benadryl (diphenhydramine) is useful mostly as a sleeping pill to be used only when you plan to sleep. You need a diagnosis and better treatment. If it is dermatitis you will benefit from prescription steroid cream. Meanwhile you can try otc Hydrocortisone cream. Zyrtec ( get generic) is effective for hives.

Blood vessel: With painful rash leaving a bruise, a vasculitic process must be ruled out. You need to consult a dermatologist to get a skin biopsy since the problem is spreading and may involve other organs as well.