I have itchy skin on my thighs during physical education class, especially when i am sweaty. is this skin rash?

Skin rash: Itching with physical activity that causes one to sweat is not uncommon. This may be from irritation from your clothing or from the sweat itself. Your thighs are obviously sensitive. Do you see a rash when the itch comes? If it's red or bumpy, it's a rash. If you don't see anything, then it's not a rash, just an itch.

Fungus?: It sounds like a fungal infection, commonly known as jock itch. Use an antifungal spray or powder, such as gold bond or desonex and see if it helps. If not, see your physician.

Likely from friction: There are many types and causes of skin rashes. Several types of inflammatory conditions of the skin, allergic reactions, and sometimes bacterial, viral or fungal infections can cause rashes on the skin. Insect bites can also be the cause of a rash on the skin. Have it evaluated by a professional and get the appropriate treatment.