If 45 days is sufficient break between taking augmentin? unfortunately my gps prescribed me amoxicillin four times in last year. (last on 14th may). now i have sinusitis (levofloxacin doesn't work well in 14 days) and prescribed once more augment

Yes, but: Yes, if it was effective last time, it should be effective now. But, with recurrent sinusitis, you should see an ENT surgeon to see if there is a mechanical obstruction which can be fixed endoscopically. Better long term plan.

Yes is fine : however make sure that underline reason for sinuse infections are also addressed. Like post nasal drip and sinuse allergies.