Your symptoms suggest that, if you truly do have pneumonitis (pneumonia) it is either of a non-infectious variety or
infectiousInfectious endocarditis
Infectious mononucleosis
Infectious mononucleosis #3 but not sensitive to amoxicillin. In either event you need to be reevaluated, without delay. The left arm pain is not typical of pneumonitis and may be a cardiac symptom, perhaps induced by the strain of your pneumonitis.
Finally, having been in Kenya, your chances of having amoxicillin resistant pneumonia are significantly increased. If you have pneumonia, the longer you continue with inadequate treatment, the more difficult it will be to recover quickly.