Hello and welcome to HCM From your history and description, you do seem to have developed an irritant dermatitis , probably to the cleaning or antiseptic substance used before or during surgery. It can also be to adhesives or bandages applied. The reaction can spread to different parts of the body. In any case, continue the benadryl for a week or so till the rash clears and no new rashes appear. Along with that, also apply a calamine lotion 2-3 times a day to soothe the skin. If the rash is severe or actively spreading, use a mild steroid cream for 5-7 days and stop. be careful not to use it at the surgical sites and only on rashes. Do keep in mind that the allergy could also be to any drugs, ointments or other medications you may be on at this time. So it is important to avoid any trigger factor to make sure it clears without recurring. Consult a dermatologist in a few days,if you see no improvement or see increase in spite of treatment. They can examine the exact status and also decide if you need any blood or skin tests. Use a mild soap. Clean with water and mild soap if necessary. Avoid harsh chemicals. Hope this helps you.