Brief Answer:
Intergluteal dermatitis.

Detailed Answer:
Hi.
Thanks for your query and an elucidate history.
Read and understood your problem that you had suffered from similar problem 2 years ago.
Now you have developed a small bump that within 12 hours advanced to the size of a quarter, is bumpy, skin looks to be thickened, weeps clear fluid that scabs. This is about 2 inches from anus and near the crevice between the buttocks.

In my opinion, this is a condition of dermatitis in the intergluteal dermatitis.
The exact cause of this condition is not known, but this is treatable and can be cured.
It usually starts as a itch. This is probable due to inability to clean up this area nicely with water, retention of the sweat, soap and so on.
The itching causes small injuries and mild infection. The area may weep, gives fluidly secretion and causes more itching , particularly at night.
Patients starts using whatever ointments are available or suggested by friends, family or local Doctors. Feels good, but the disease remains there to recur or have vexing and vanning.
Many patients have some or the other problems with digestion or motion.

I do advise all such patients as follows::
-Clean the area with plain water as frequently as possible.
-Apply liquid Povidone Iodine locally to the whole area and allow it to dry.
No other ointments or lotions/ soaps / chemicals are needed.
-A small course of an antibiotic and Metronidazole for about 5 days ( you need a prescription please- of a local Doctor)
-This is basically a disorder due to deficiency of vitamins and minerals that the integrity of the skin is lost. So you have to have therapeutic dosage of Vitamin A and D and to continue as multivitamins which are available as anti-oxidant medicines for about a month or so.
-I have seen the best results in almost all patients with this therapy.

You may please consult and get examined by your Doctor and discuss these points.

Take care, get well soon and permanently.

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