It is very itchy on my inner thigh. The skin is darker in that area. It gets bad when it is sweaty?

Hyperpigmentation. If you have heavy thighs and sweat heavily in that area this is inflamed skin which from a combination of itching and rubbing has developed a thickened skin with dark color. This needs o be diagnosed and treated. The color is difficult to lighten completely and will not respond to over the counter medications.
Itchy thigh skin. There may be a yeast rash called tinea versicolor. Dark, moist and warm skin may foster the growth of normal fungus on the skin. It can cause a slightly darker skin color and scaling. See a board-certified dermatologist to diagnose the problem and treat the condition.
Could be.... Tinea = a fungal skin infection that notoriously likes to grow/live in dark, warm, moist areas - such as you are describing. It can darken the skin and is best treated with keeping the area as dry and cool/aerated as possible, staying away from Hydrocortisone cream (which may lessen the itch - but can help the fungas grow) - should be treated with antifungal creams/powders daily - all are otc.