What kind of antibiotic is good to take for a upper respiratory infection or sinusitis? i'm on amoxcillin now is it going to help me?

None: Most upper respiratory infections are viral. As an infectious disease specialist, I try to avoid antibiotics as much as possible. If your doctor truly believes that your infection is bacterial, then amoxicillin may be reasonable to start with, other options are Augmentin (amoxicillin and clavulanate) or if you are not pregnant then levofloxacin or Bactrim.

Probably: Although most Upper respiratory infections are caused by viruses and antibiotics are not effective against viruses. If a viral infection lingers long enough and you develop more severe symptoms such as higher fevers headaches productive cough, it may indicate a transition to a bacterial infection, at which time an Antibiotic will absolutely help.