Pain under right armpit when I breath deep or lift my arm up

Has your doctor had a look at it?

Not yet,its only happened last couple of days.the pain feels like a stitch from running

Typically my doctors say either immobilization,ice/heat(whichever would suit the needs)and waiting to see if it persists.

More than a few days,I see them no matter what,a sprain or strain will lessen in pain by degrees over a few days,a tear in muscle or something more severe may or may not lessen and might require more attention from a professional.

I see my GP when something is longer than 3-4 days old,he can then refer me to whomever the specialist would be in the field it would be involved in.

Taking care of yourself by following the advice of the professionals is your choice,they(and we) can only advise in our experiences.

I am not a health care professional and this isn't medical advice,it IS opinion from my experiences.