Hello and welcome to HCM,
A golf ball sized bump under the armpit is most likely to be due to lymph node enlargement.
However, a clinical assessment is required to know the nature of the bump.
Clinical assessment may be followed by an aspiration cytology.
In aspiration cytology, a fine needle is inserted into the lesion and cells are aspirated. The cells are spread on a glass slide, stained with appropriate stains and then examined under microscope.
This investigations will determine the origin & nature of the lesion and thus help to plan further management.
Mosquito like bumps all over the body could be due some kind of infection.
Diarrhea in an 18 month old is suggestive of a
gastrointestinal infection.
Since,
dehydration is a major risk factor in children with
vomiting and diarrhea thus hydration should be maintained by giving fluids like ORS.
Nutrition should also be maintained with home made light food.
For definitive treatment of infection, clinical assessment is required.
So, consult your
pediatrician at the earliest.
Thanks and take care
Dr Shailja Puri