skin infection, usually caused by staphylococcal bacteria. Possible blockages of the sweat glands. Hair follicle that have gotten infected. Here is an excellent site that explains this more in detail as well. read here
Since you have more than one.. you really should see your doctor. A course of antibiotics will be needed. As far as thyroid, a change in hormones can cause these to occur as well. Which you can also have your doctor do a full blood work up.
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