I do not think it is a good idea to try it. You may have allergy to it, and it is quite dangerous.
I would suggest looking into dental school (such schools usually either charge 50% of what normal practices would or they may provide you with a sliding scale type of payment) around your area or possibly a free clinic.
Your pain may be caused by something different from your husband. Amoxicillin is an antibiotic, but I would not advise you to try and borrow his medications.