Sir yesterday I had oral sex with my girlfriend. I Fingered her vagina. Till
Now we never had intercourse. When I fingered her yesterday she
Complained of pain in her vagina. I stopped it and in morning she
Called me and said its still complaining. Sir what may be the reason
For that. I care for her a lot. She saidit is paining as if a pin is
Pricking her in der.
I'm looking forward to you reply sir.
Thanking you.

There is no way we can know. Maybe a fingernail cut her. Maybe she is a virgin and her hymen broke and it hurts (it shouldn't more than a little). But maybe something else is wrong, such as an infection. So she has to go to a doctor.

Yes, it can be many things, an infection, often a scratch from finger. If pain continues she will need to see the doctor