I.G.
My daughter had perioral dermatitis last summer - it was a mild to moderate case. Her pediatrician advocated a wait and see approach as long as it was tolerable. We used some barrier cream in some areas (she was still using the paci, so under the shield was worst) and it cleared up without any abx or topical steroids. Took about 2 months to be completely gone.
Apparently abx do not always work, and steroids can actually make it worse... but it really depends on how bad it is. There are other topicals that can be tried, I would get a second opinion.