Hi Dawn,
It's very likely that the skin disturbance described is the result of contact with stinging hydrozoans or anthozoans, such as the so called "stinging hydroids" or so called "fire coral."
It appears you were aware of the envenomations at the time they occurred, but didn't develop a full blown reaction until about 10 days later. Such delayed reactions are not uncommon. Just 4 days ago I heard from a chap who was diving the Caribbean and received stings while descending an anchor line (notorious for growing an abundance of hydroids). While reportedly aware of the stings when they happened, a notable allergic skin reaction wasn't evident until about a week later.
As Vlad the Impailer pointed out in his post above, it is not uncommon for the rash, itching and burning to recur after the signs and symptoms initially subsided. This is because antigenic material (e.g., tiny fragments of coral or hydroid feathers) can remain in the wound. Also, a cyclic immune response (redness, inflammation, itching, and swelling, itching or burning) can persist for weeks after the incident, sometimes longer.
In the meantime, some divers find the best bet to be an OTC antihistamine like loratadine (Claritin, 10 milligrams) or cetirizine (Zyrtec, 10 milligrams) taken as directed, although they can be mildly sedating. A topical preparation such as Benadryl (diphenhydramine) cream/ointment can help reduce itching. However, essentially gentle care and tincture of time are the best medicine.
In serious cases prescription antihistamines like Atarax or Vistaril, or oral steroids such as prednisone, may be directed by a doctor, but the situation described does not appear to warrant such treatment at the moment.
The condition should be carefully monitored and if the reaction appears to be getting significantly worse, or infection seems to be developing (always a worry with these scrapes/rashes), a dermatologist should be consulted as quickly as feasible.
It should be mentioned that the immediate treatment of such stings is rinsing the affected areas with copious amounts of plain white distilled vinegar. It's surprisingly effective, but will do nothing beneficial 10 days after the envenomation.
Best of luck.
DocVikingo
This is educational only and does not constitute or imply a doctor-patient relationship. It is not medical advice to you or any other individual and should not be construed as such.