I'm taking bactrim (sulfamethoxazole and trimethoprim) for a sinus infection because i'm allergic to penicillen. is this a strong and effective antibiotic?

Possibly not: Most sinus infections do not need antibiotics. Based on the 2012 IDSA guidelines, Doxycycline is a reasonable alternative for first-line therapy and can be used in patients with penicillin allergy. A respiratory fluoroquinolone (levofloxacin or moxifloxacin) is another option for penicillin-allergic patients. Bactrim (sulfamethoxazole and trimethoprim) and Macrolides are not recommended because of high resistance rates.