Thank you very much for the useful information Kirsten.
Most likely this is not ring worm infection rather can simply be HIVES, which can appear due to an allergic reaction such as from drugs, garments, insect bite etc. Even some times they can appears during periods of physical and mental stress and then go away.
Sulphasalazine can also give a person such various kinds of rashes, some very benign and self limiting (like you have) and some times can give serious skin reactions.
At this point, i will suggest you to wait and just watchfully monitor this rash over next few days or a week. So how this behaves; and in case if this does not disappear, or start getting worse have this examined clinically by a dermatologist.
There is no harm in trying 1% hydrocortisone ointment over this (apart from the ring worm ointment you are using) for few days---may be it helps.
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