Thanks for the query.
You might be suffering from cholinergic urticaria
It is a condition characterised by development of red itchy rashes when the body temperature raises.
you need to take the anti histamine
tablets on a daily basis.
As and when required intake wont help you.
Please meet a dermatologist
and discuss regarding this.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.