There are several risks to taking expired medications. First you cannot be sure that the medication is still effective. Although medications do not simply stop working the minute they expire, they do gradually break down; so, depending on when the medicine expired, its strength could be significantly reduced.
Second, the dose of medication that is on your friend's bottle might not be the same dose of medication that you require. Different conditions are treated differently (same medication, but different doses and for different lengths of time). Therefore, it is never recommended to take someone else's medications; you should have input from a doctor
Finally, you may not need an antibiotic at all. Antibiotics have multiple side effects, including diarrhea
and the risk for resistant bacteria developing. Many sinus - like symptoms do not need antibiotics but, rather, are treated conservatively with decongenstants, nasal irrigation, and waiting it out. You would not want to take an antibiotic without being sure you had a sinus infection, something only a doctor can tell easily with a physical examination.
I suggest that you try to get in to see a primary care doctor
. You can explain to them your insurance issues; many department store pharmacies offer very low cost prescription medication programs for those with limited or no insurance.