Stomach issues?

I'm 17 & I have acid reflux. I seem to go through these cycles where I'll have stomach pains and stomach aches for about a week or so, and then I'll be fine for the next few weeks. Today -- and for the past few days -- I've had the same stomach upset and nausea. I just had a bowel movement that was tan & dark brown, which was a little strange. I'm going for a barium swallow on March 6th, but is this something that I really need to worry about?