Is my stomach discomfort caused by my anxiety disorder?

I have been diagnosed with anxiety disorder last month and have experienced several physical symptoms of anxiety, during my trip to Japan last week I had acid reflux in the first few days, I could feel the food going down my throat and have some burning sensation in my throat. It went away after a few days although I still occasionally feel the throat tightening. Fast forward to a few days after the trip, I started having some discomfort in my stomach which locates from the upper left to my lower abdominal area, I really have no clue which organ is causing the tight feeling. Also I have been having diarrhea for the past few days and I noticed that my stools have some dark brown or black specks in them, I'm so anxious due to this cause it can indicate inner bleeding, but I don't think I was feeling anxious when the stomach symptoms occur, so I'm not sure if it's stomach distress caused by my anxiety disorder or i actually have some serious health issue. I have already went to the hospital to check my heart and everything came out fine so I doubt that it'll be related to my heart but what if it's really something serious??? Someone please helpsad

Anxiety can cause all kinds of symptoms, I now have to watch what I eat because I have acid reflux and anxiety isn't much help, you may need to have your stomach looked at just to be sure nothing else is causing your discomfort, best of luck and hope you feel better soon