Sinus infections are not usually treated with the penicillins anymore (like amoxycillin), because there are stronger meds out there that work a lot better. In fact, doctors don't tend to prescribe it as much as they used to.

For the most part, they go with drugs like doxycycline or zithromax for sinus infections, because they tend to target the cause of the sinus infection a lot better.

That being said, since you're allergic to penicillin, you should not take ANY deriviative of it, including amoxycillin. Your mom is stupid for even suggesting it, since i'm sure she knows about your allergy to it.

Sinus infections really do require a doctor's care, so if there's any way your mom could pay for you to go to a walk-in clinic instead of trying to kill you with a penicillin-based antibiotic, that would be great. I mean, seriously... She's really stupid.