There are a few different reasons that the testicles may itch. Probably the most common is simply irritation of the skin from moisture and chafing from clothing. This is very common especially if you have been exercising regularly or otherwise sweating, but it can occur at any time. Keeping the affected skin clean and dry, and the application of a moisturizing lotion, should clear things up easily.
A fungal infection is another possibility. Fungal infections of the groin, called tinea cruris or jock itch, are also very common - fungus tends to grow well in moist, dark places, such as the skin of the groin. Symptoms of a fungal infection of the groin include redness of the skin, together with severe itching and flaking; there may also be some odor. Fungal infections can sometimes respond just to skin hygiene and keeping the skin dry; however, many do require anti fungal creams as well in order to be totally cleared up.
Either way, you should set up a visit with your primary care doctor
to see if an additional treatment might be needed.
I hope you are feeling better soon.