Since I don't know your sex, I am going to assume you are female as most males would say masturbating instead of fingering.
So for a female, she will be more horny just before her period then at other times. It is usually times like this where a female might finger herself or use sex toys or if old enough and has a boyfriend-then having sex.
I have never heard of a female having pain in stomach anywhere just from fingering, even fingering with an orgasm. This must be a coincidence that you felt pain right after. The only random pain you could feel is period cramps. Some get these before the period starts. So if you being horny was what prompted the fingering, then this could be an explanation and would be a normal pain, nothing wrong.
If you have pain without a period starting and its been a day or two, and the pain is either constant or comes and goes, it is time to see your Dr. This has nothing to do with sex and the pain would be something not normal, perhaps harmful in the long term. So if this is the case, see the Dr. Tell Mom that you have a pain that won't go away so she can make an appointment. Again, you don't have to say it started when you fingered yourself. You can share the day and time of day it started so they know how long its been, and that's all that's necessary.
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