I don't think that antibiotic is needed
Thanks for asking on this platform
I have gone through the query and do understand your concern.
During initial months of life change in color, consistency or frequency is quite common.
I won't get worried if baby is otherwise active, passing urine, accepting feeds well and there is no other significant abnormality.
Antibiotic is needed only if there is blood or mucus in stool(suggests bacterial infecyion). Even diarrhea(loose stool
) in this age is commonly due to virus and does not need treatment with antibiotic.
I would not suggest antibiotic for transient change in frequency, consistency or frequency of stool.
You may give probiotics which helps in maintaining normal gut flora
Antibiotic does not affect vaccination
as vaccination in this age is mainly for virus like rotavirus
I hope this helps.
Please let me know if you have any more questions.