Strange situation. I guess I'd start by talking to the nurse at school, or even the coach, who might know something about injuries. If they could provide some input, then it might encourage your mom to have something done. Do you have insurance? I am wondering if money could be an issue...and if maybe your mom couldn't afford a series of doctor's appointments, which would probably include x-rays and the like to figure out what is wrong.
Do you have anyone at school to talk to? Perhaps your ex swim coach?
It's hugely important that you ignore your mother and get medical help - you need an x-ray and most likely some physiotherapy.
Now is the time to get it sorted, otherwise you'll regret not doing so when you get older.
You must go to the doctor and insist on x-rays so you know once and for all what is wrong, then what is needed as treatment.
Your leg is ****** and those kinds of problems don't ever go away.
Don't they teach kids to use "periods" any more?