Can doxycycline used for sinus infections?

Yes: If the infection is caused by bacteria, Doxycycline is an effective antibiotic -- however, most sinus infections are viral and will resolve on their own with supportive treatment and time.

Not great: Doxycycline would not be my first choice of antibiotics. I agree that if you feel like you have a "sinus infection" and it has been only 2-3 days.. It may in fact be a viral respiratory infection (common cold). If those symptoms last for more than 7-10 days then by definition it is a sinus infection and i would get it treated wtih antibiotics at that point.