Chris, I reread your post. I hadn't noticed the part about you taking some amoxicillan that you had around. Definitely, listen to your mom and get a prescription.
You have to be sure you've got enough to knock out that infection. You also want to be certain that it's not much past the expiration date. I'm assuming that it's not the liquid form of amoxicillan. If it's in the liquid form, I would suspect it's lost it's potency.
I don't want you to end up with some nasty infection that end up being a bear to treat.
And I'm sure your mom has told you, if you have strep, you must take the appropriate antibiotics for the entire time prescribed.
Now you've got online friends nagging you too.