im not sure if you have a friend who could take you to a local clinic but you need to go get medical help maybe you could go to your local fd as they may be able to help you.
I had a lump on my arch like that after I had an accident quite a few years ago. It was painful. All I can tell you is that I do still have a bit of a lump there, but it no longer causes me any pain or other issues. Hopefully yours won't either after a bit more time.
You should have this injury looked at...you're too young to have an injury and not take care of it! Sounds like you're very athletic and will want to be skateboarding in the future, so this should be checked out to determine if you've done muscle/tendon damage, or even have a occult fracture of one of the bones in your feet. Remember, this foot will be with you for the rest of your life, so take good care of it! Have your Mom or some other adult you trust take you to the doctor...Good luck!