I am having rashes on my thing ( back) part only for past one month, the rashes will be there for one hour or after taking avil tablet it reduces and becomes normal skin. I have itching on the legs. Today the rashes started on my chest. This subsides after one or two hours. Please advise as why I get rashes for a period of one hour and it subsides after that period.

There are several kinds of rashes:
Allergic reactions to heat, direct sun, synthetic clothing, wool, too tight clothing, dirt, dust, dust mites, some foods.
Fungus.
Yeast.
Bacteria.
We can't tell you which of these yours is. I doubt that it is bacterial.