This is very common, and can occur between the legs, around the scrotum in men or labia in women.
It can be called lots of things like jock itch, thrush or candida. Symptoms are: itchiness, can be red and possibly raw looking. This is very treatable. Firstly, wear loose fitting underwear like boxer shorts (it's important to prevent a warm/moist environment that will make the condition worse). If spending a lot of time seated, try to sit with legs apart.

Various preparations might help to sooth or dry out or stop a fungal infection. These include: tea tree oil (to act like a drying agent), paw paw ointment for soothing, miconazole cream or other anti thrush cream from the chemist. If these options do not help then see your doctor for a swab and either some more cream or oral tablets. Probiotic intake has been known to help. You should also consider reviewing the amount of sugar in your diet to reduce it.