However, your description of feeling pressure on your chest and the difficulty breathing - it would seem to be related to your lungs - lung infiltrates often feel like that.
Pneumonia for instance. However, it could also be that an
injury to your ribs or muscles has made it difficult to breath because of the pain.
How long has this been going on? Do you have a cough? If so, is it productive? (bring up mucous) Have you had any respiratory problems in the recent past? A cold? Fever?