You didn't say how long you've had the lump, but anything that hasn't cleared up in about 3 weeks should be seen by a doctor.
It could be any number of things: an inflamed taste bud, a blocked salivary gland, a small cut on your tongue from a chip shard. To find out for sure what it is or isn't you really need to go to the doctor. Please ask your mom to get you an appointment.
Let us know how it turns out.