Itchy, sore, red (and whitish) anus & butt crack x5 days after taking Aumentin. Abx caused diarrhea, so had to wipe a lot. Just irritated or candida?

Both. Could be both. Augmentin (amoxicillin and clavulanate) can be very irritating to the bowel and can cause yeast. Use both an anti fungal medication and a barrier cream and keep the area irrigated in the shower. If not better, see your doctor for an exam. All the best.