Questions about a mole or new skin lesion are best answered by a dermatologist
In general, the guidelines for when to seek medical care about a mole or skin lesion can be summarized in the acronym ABCDE.
A stands for asymmetry. If you were to draw a line through the center of a mole or freckle and the two halves were not symmetrical, you should consult a physician for evaluation.
B stands for border. If the border of the mole is blurry or or jagged, you should see a physician.
C stands for color. Normal freckles or moles or typically one color throughout. Normal freckles and moles are typically a single color throughout.
D stands for diameter. If a mole changes suddenly in size, it should be checked by a physician. Likewise, a physician should be aware of any mole or skin lesion that is larger than about 1/4 of an inch (5mm or so). some moles can be larger than this, but they should not change in size over time.
E stands for elevation. A normal mole or freckle will be flat. If the surface becomes elevated or protruding, it should also be evaluated by a dermatologist.
Any one or combination of these changes should prompt a visit with a dermatologist for evaluation and likely biopsy