The pain in the armpit could be because of the pleural reaction in the chest .
Pleura is the covering of the lung and when there is infection in it it may cause pain in moving ie while breathing or while coughing.
YOu need to get physician consultation as this can be ruled out by examination . Otherwise there can be lymph
node enlarged which also can be ruled out by examination.
continue with antibiotics and take anti tussive medication too.
In doubt do reply.