Under eyelids if there's a small pimple like ...what is that?

Take note and monito: It is likely a pimple or a blocked gland in your skin. Take note of its present size(a photograph in cell phone may be even better). If it remains unchanged for 3-6 months it likely can be left alone unless you wanted it removed for cosmetic reasons. if it grows in (doubles in size) then you need to see a physician for medical examination. It is also likely that it will go away on its own.