swelling, goitre
癭 centers on an abnormal lump or swelling on the body, especially a goitre in the neck.
癭 combines 疒 (sickness) with 嬰, which likely contributes the sound and may relate to the idea of something encircling or swelling, as in a goitre.
The sickness enclosure 疒 wraps around 嬰, which looks like a woman with a swollen neck. Picture a woman with a visible goitre, the swelling caused by illness.
For エイ, imagine an 'A'-shaped swelling on the neck: the letter 'A' sounds like エイ, and the goitre bulges out like the letter A.
cecidium; gall