Webster 1913 uses the word pustule, one of my personal favourites for invoking an image of a pus-filled nodule. A wheal is, more correctly, a small, burning or itching swelling on the skin, as from a mosquito bite or from hives. In hives, wheals occur in crops which can last a few days or much longer. Yuck!

Wheal (?), n. [OE. whele, AS. hwele putrefaction, hwelian to putrefy.]

A pustule; a whelk.

Wiseman.

© Webster 1913.

Wheal, n. [Cf. Wale.]

1.

A more or less elongated mark raised by a stroke; also, a similar mark made by any cause; a weal; a wale.

2.

Specifically Med., a flat, burning or itching eminence on the skin, such as is produced by a mosquito bite, or in urticaria.

© Webster 1913.

Wheal, n. [Cornish hwel.] Mining

A mine.

© Webster 1913.