Hi. How old are you? You received oral sex? Do you have a vaginal discharge? Most likely this is something like a yeast infection. Which itches. So, do you have a vaginal discharge and what exactly is itching? The whole genital area?
You could have a yeast infection or bacterial vaginosis, both of which can happen without any sexual activity. The oral sex may have triggered it, but so can many, many other things. Can you tell your mom that you think you may have a yeast infection and have her take you to the doctor? Do you think she'd let you go into the doctor alone?
The chances that you'd get an STD from receiving oral sex are really low, but you should be seen to make sure you don't have bacterial vaginosis, which needs antibiotics to clear up.