Hello! From the history, it seems like allergic reaction to infected or possibly polluted water while swimming. (the photos section shows there are 3 photos but nothing is visible).
Just for your information, a swimming pool rash is common either swimming in either chlorinated, polluted or infected water. The skin regions exposed to pool water containing excessive amount of chlorine may also lead to such rash. Although chlorine is a necessary element in swimming pools in order to kill bacteria but it may lead to allergic reaction to some sensitive skinned people. The best precaution is to avoid chlorinated water for a while to let the skin recover from the chlorine exposure. Also, shower with plain water and anti-bacterial soap before entering the water and after leaving the swimming pool is recommended.
Another factor which can contribute to such rash is water infected with Pseudomonas aeruginosa. This is less likely due to its acute presentation. However, chronic infections are known as well and respond to ante-bacterial treatment. This treatment can be started if culture of your rash scrapings is positive for this bacterial infection.
Sometimes the cause cannot be identified despite several tests. Also, sometimes, if the rash does not subside, it is best to get your blood sugar tested. High blood sugar predisposes one’s body towards bacterial and fungal infections, allergies, and eczemas.
The general treatment options for such rashes are antihistamines like cetrizine (non-sedative antihistamine) or avil (it has sedative side effects), which are available over counter for general allergies, use of over the counter corticosteroid creams, cool compresses, bathing in water with baking soda added, or use of various anti-itch lotions that are available without a prescription such as Aveeno or Calamine lotion. You may also take Vitamin C along with the above treatment. Vitamin C is a general anti-allergy supplement.
Another possibility is that the rash and swimming pool are not connected. In this case, it could be allergy to anything—swimming costume material, pollen, animal dander, any personal care product you used etc.
While I have outlined some treatment options for you, possibility of fungal infection should be re-tested. Sometimes after a course of oral and local anti-fungals, your KOH test may not be positive. A comprehensive investigation is required keeping all the points in mind. Please consult your doctor regarding this.
I sincerely hope you will find this information useful in your journey towards better health.
Hope you get well soon! Good Luck and take care!
I attached 3 pics in my profile under "rashes" album for any doctor that wants to see