It does sound like eczema, or possibly psoraiasis. Try chaning your clothing material, your shower gel, and cutting down dairy produce and sugar in your diet - any or all of these will help to alleviate either condition.
what you can do before seeing a doctor is, see if soap or any cleaning related materials are suit to yourself, it's good to know your skin type, sometime, cleaning overstayed-old skin tissue makes some itchy feels, because new tissues are getting contact with oxygen.
....none of above ?. go and see doctor.
It is more likely to be overheating. I too get this. If you kneel, sitting on your feet for a particularly long time, you will itch behind your knees. This is why I think it is related to trapped body heat.
Ask your GP to do a Full Blood Count (FBC) - itching is associated with iron deficiency anaemia (blood too thin) , but itching after a shower or hot bath is particularly associated with polycythaemia (blood too thick).