Itchy groin and rashes in places on the scrotum (not that easy to see though), what is this?

"jock itch" The most likely cause of this is a fungal infection. The over the counter medications that treat athlete's foot can also eliminate this.
Scrotodynia. Men have described pain, burning or abnormally sensitive scrotal skin over a prolonged period of time. There are no abnormalities visible when the scrotal skin is examined. However, similar symptoms may arise in patients with visible and named skin disorders. This condition is called scrotodynia.

Related Questions

Note, the rash is red flat dots, and some are dry white patches, itchy, around groin, itchy anus and itchy scrotum, doct says it was fungi, is true?

Can't tell. Without a direct observation, I would not second-guess your doctor. However if the problem persists and his treatment failed, then you need to consult a dermatologist.
We can't diagnose. This with the available info. This rash needs to be visualized & a history needs to be obtained in order to make an accurate diagnosis. Sometimes lab testing or biopsy is necessary.