You should tell your mom. It may be an area kinda like a pimple, you can try a warm compress to the area to help draw it out, this will also ease the pain. Once it does come out, you'll probably have a little bit of bleeding when you wipe, this is normal. But tell your mom as if it's something different, you really need to see a doctor.
My vagina has a strange bump inside one of the lips. I am a virgin. It is painful when I touch it. I think its growing
If the spot seems to be growing, increases in pain, or lasts for more than a week you need to make an appointment with your healthcare provider. In most cases, if you are 16 or older (depending on your state and healthcare provider's policies) you should not need to have your parents make you an appointment nor will they be informed of any diagnosis or treatment.
If you do not have access to a private healthcare provider, contact your local Planned Parenthood, reproductive clinic, or free clinic. They can refer you to another clinic, if needed, or treat it themselves are a reduced cost to you. Again, if you are over 16, depending on your state, you should not need your parents approval, or consent. If you are under 18 check with the clinic on what their policies are concerning parental involvement before you make an appointment.