Brief Answer:
I would like to rule out streptococcal dermatitis

Detailed Answer:
Hello

Thanks for the query
I have gone through the images

In this situation where there are initial erythematous rashes which later on changes into vesicular rash and then denudation of skin with a well demarcated border and excessive irritability in peri anal area in the presence of green colored mucoid stool, I would first like to rule out streptococcal(bacterial) dermatitis.

There can be different causes of rashes in the perianal area in this age.
The most common is irritant diaper dermatitis.In this condition there will be redness around the perianal area with irregular border.The irritability and pain is much less common than streptococcal dermatitis.
The next common cause is candida dermatitis(fungal) in which in addition to the irritant dermatitis there will be white color satellite lesions.


The sialoderm ointment containes calamine and zinc oxide and mainly used in irritant dermatitis as it has soothening properties.I would suggest you get a scrap test done in which a gentle scrap through a swab is done followed by its test to find out the causative organism.Oral antibiotic like cefuroxime or amoxycillin with topical antibiotic like mupirocin along with sialoderm will provide relief.These are prescription medicine,please get it prescribed.
I would recommend you to consult a pediatrician to get the test done and discuss about the possibility of streptococcal dermatitis and management accordingly.Some analgesic like ibuprofen/paracetamol combination may also be needed.Continue giving breast feed and watch for signs of dehydration like urinary frequency.

I shall be glad to answer if you have any more query.
Wish your baby speedy recovery
Regards

---