I have a sore on my arm that is looks like a bacteria infection. any way to tell if this is a bacteria?

Yes depending upon : Having symptoms like: pain, redness, discharge (yellowish/greenish or reddish with some blood). Tenderness around it, or red streaks going up from it towards the elbow or armpit, & these sites may be painful & be tender to touch. Fever (99-102) maybe present, with chills, or have a history of these symptoms. Your doc can confirm by testing a swab from the sore to grow the bacteria causing it.