Is it possible if i only take clarithromycin for pneumonia for 3 days, the infection remaining clears up after that without antibiotics? just asking.

Yes...but: The short answer is yes. But you should complete the course of therapy or return to your doctor if you don't tolerate it. You also run the risk of producing a partially treated resistant bacteria. Just take your medications as prescribed. The medications don't work in the bottle on the shelf in your bathroom. If you aren't going to take them, discard them appropriately.