Hi,
It could be eczema, sweat dermatitis, allergic reactions or eczema.
You need to wash the areas several times with fresh water. Do not use any cosmetic products at the sites.
Apply calamine lotion at the site of the lesions and see if it helps. You could take some oral antihistamine medications like cetrizine or loratadine. You need to maintain a good personal hygiene .
Anti-itch drugs, often antihistamine, may reduce the itch during a flare up of eczema, and the reduced scratching in turn reduces damage and irritation to the skin.
For mild-moderate eczema a weak steroid may be used (e.g. hydrocortisone or desonide), whilst more severe cases require a higher-potency steroid (e.g. clobetasol propionate, fluocinonide).
Eczema can be exacerbated by dryness of the skin. Moisturizing is one of the most important self-care treatments for sufferers of eczema. Keeping the affected area moistened can promote skin healing and relief of symptoms.
http://en.wikipedia.org/wiki/Eczema
It would be advisable to consult a skin specialist for your symptoms and a proper clinical examination.
Let us know if you need any other information and post us on how you are doing.
Regards.
Very hard to tell what a rash is without seeing it, so yes I so suggest you show it to a doctor. If you are feeling unwell with it it could be mabye chickenpox, which means you are infectious and need time off school etc. Or it could be an allergic reaction, or a skin condition. Really you need to have this checked out, particularly as it seems to be spreading. Make an appointment with your doctor. They will also likely be able to prescribe you treatment for the itching. Get well soon.