Hi,
Based on your post it appears that this may be a case of Milaria Rubra.
Miliaria rubra, sweat rash or prickly heat is a skin disease marked by small and itchy rashes. Miliaria is a common ailment in hot and humid conditions, such as in the tropics and during the summer season. Although it affects people of all ages, it is especially common in children and infants due to their underdeveloped sweat glands.
Prickly heat can be prevented by avoiding activities that induce sweating, using air conditioning to cool the environment, wearing light clothing and in general, avoiding hot and humid weather. Frequent showering may also help.
Medical assistance should be sought for the first episode of a rash with the appearance of miliaria. The differential includes several conditions which an experienced practitioner should be able to recognise and may require treatment distinct from the usual measures taken for miliaria. In most cases the rash of miliaria will resolve without intervention. However, severe cases can last for a number of weeks and cause significant disability. General measures should be recommended for all patients, including moving to an air-conditioned environment if possible, avoiding sweat-provoking activities and occlusive clothing, and taking frequent cool showers.
You may find more information at: http://en.wikipedia.org/wiki/Miliaria
Best regards