chest pains came back a year after severe pneumonia

Last spring, after having a flu and making the mistake to go work out at the gym, I was diagnosed with sinnuitis and after that, pneumonia. I would have really bad pain on my left side lung and also in my lower back on the left side, even in the middle of the night. Even the slightest amount of strain or exhaustion would cause pain or a feeling of "rubbing" in lower back. This went on for a long time. I was first given Zithromax, and after that didnt help I was prescribed a 10 day course of 875 mg penicillin pills. It took me about 3 months to finally recover from this. Yet, I continued to have randomly reoccuring pain and sensation of "rubbing" in my left lung.
Half a year later, in the fall, was the last time this happened. Since then, I have been feeling great and working out at the gym and continueing on with my life normally, with no symptons what so ever.

BUT a few weeks ago, I caught a flu, that didnt seem to go away at all. It lasted for about 10 days or so. After this, I seemed to have a little trouble breathing for about 5 minutes after I did a spurt or did something that made me get out of breath. I didnt think much of this, until this was sometimes accompanied with slight pain in the chest. 3 days ago, I had to go do an overnight shift at work. The first night was fine, but right before the 2nd night, I felt slight pain again. I thought okay, its happening again, but I was certain it would go away in 10 minutes, just like it had all the other times. But it didnt. For the whole night, I had to be careful about breathing in deeply, because most of the time that caused pain. I was a little short of breathe but I tried to stay calm, and not overlyexhaust or strain myself. My body was not used to staying up all night, because it seemed to get very strained because of this. When I got home in the morning, I had continous pain on the left, sharp pain, and it lasted for a long time! I am guessing that staying up all night, caused too much strain for my body, which in turn caused the pain. I could not even lay down, for some reason, that made it worse! I took some ibuprofen and ended up getting some sleep, half sitting. When I woke up, I was feeling normal again. I have had this pain again randomly, reoccuring, during the next few days. I went to the docter, and she sent me to take an x-ray. I am waiting for the results now.

I thought that I had finally gotten rid of all the pain for good, after last spring. I cant live my life normally at all, because this pain seems to surface anytime I stress myself or dont get enough sleep, or for whatever reason. Even now, when Im typing this, I feel slight pain when I breathe in deep. If I ONLY knew what was the cause of this, if I only knew that it wasnt dangerous, I would be so better off. Why cant the docters find anything wrong? Should I go have a ct-scan taken? Please, if anyone knows anythign about this, please help me. Thanks!