Appendicitis
Appendicitis is a condition in which the appendix is infected. If left untreated, it can lead to rupture of the appendix and it can get fatal.
In the initial stages of appendicitis, you could observe a mild pain around your belly button, but this pain can spread to the upper stomach. The pain then moves to the lower-right side of the abdomen as the infection exacerbates.
The most common way of treating appendicitis is by surgically removing the appendix.
Muscle Pain
Many muscles originate or insert into the upper stomach. Temporary pains in the upper stomach can be caused by dull muscle injuries or spasms.
Soft massage and a lot of rest can reduce the pain. In some cases, using a cold or hot pack may help relieve the pain.
If the muscle ache continues for a long time, you should see a doctor, to make the right diagnosis.