Since more than 1 month i have mild sinuses pain (when hot weather) and pressure (sometimes frontal,sometimes ethmoidal etc.). levofloxacin and augmenting didn't help but clarythromycin after 11 days (2x 500) help a little.should i take it up to 14d?

Sinus: it is ok to take for 14 days. You may want to try a nasal spray like Flonase to help with the inflammation in your sinuses too as all sinus issues are not infections.

If that's how it's..: ...prescribed & you are feeling better & not having side effects, then YES. Keep in mind that problems other than (or in addition to) infection can cause sinus pain & pressure. Sinus & nasal allergies, dust & other environmental pollutants and congested nasal & sinus passages are among the potential factors that can contribute to symptoms like yours & may need to be treated.