Please see the doctor.
It could be any number of things - if it'S.strep, it'S.a bacterial infection that will need antibiotics. There are S. many different antibiotics on the market, some are safe for nursing mothers, others are not. Your physician should know (and you should always check with your pediatrician to be safe).
Worse case scenario, you can pump while you're on the antibiotic and provide your baby either frozen milk or formula. I had to do that for a few days with my son while nursing to take naproxen which was not safe for nursing.
A bacterial infection that has gotten to this point is not going to be cured by a home remedy, and you're already contagious to your child. Strep in a baby is much more serious than it is in an adult because of their immune systems not having the appropriate antibodies to combat it.
Please call your doctor and get to feeling better soon.
Mary'S.Magic Mouthwash is usually for more mouth sores. It does have antibiotics in it depending on how the physician orders it to be made - it has to be compounded by the pharmacist based upon physician orders.