Thanks for the query
Fluid filled lesions at 2 months of age not progressive in nature and not associated with fever
or any other manifestation is seems to be benign one. Yes it may be due to some kind of allergy
one of which is soap. There are so many other condition which may manifest like this and they are usually self limiting in nature.If the lesions are not increasing in number and size, if it is not pus filled then no need to worry. But if you notice any change then as it is persisting for more than one week consult your doc. for proper evaluation.
I hope this answers your query well
Wish you and your family good health