Diaper rash 2 weeks

I noticed a little red rash on both side of her butthole, I don’t leave her sitting for more that 5 minutes without checking her diaper so how is she getting a rash? I’m so upset I feel like a bad mom... I even put a and d on it before this happened and now trying destin. She has been pooping a lot more so if that why? How to help it!??