It sounds like it could be a cyst. They will usually go away on their own. You can google: lump on vaginal wall. You should get some information to pop up. I agree with the above poster, you should be seen by a doctor just to make sure everything is ok. Please let us know how you are doing.
If you are concerned you can go to the ER. It is against the law to turn someone away They will usually have some type of program that will help you pay your bill.