Breast pain. For stomach problem etc.

I am experiencing a slight pain in my left breast .. very mild and it usually is after my period and remains for a week or two .. this is happening from sometime now .. upper rib also pains sometime.. to mention pain is very mild .. I feel I keep on thinking and psychologically I feel there is pain and when I am busy in something I don't feel any pain I have stomach problems like gastritis and get a lot of acidity .. so I feel this left side discomfort is because of stomach issue and nothing to do with breast .. coz as soon as I feel gassy I get slight pain .. my eating schedule is not good at all .. have been eating all unhealthily and that too from outside .. can I get any good advise here as to what to do .. what medicine to take for stomach problem etc .. TIA