What Causes Nausea After Taking Macrobid?

I ve been taking Macro bid 2 times a days since Tuesday for a UTI and I know it causes nausea, I get pass that by taking it with food. But now the past 2 days when I eat about 5 hours later I experience TERRIBLE EXCRUCIATING PAIN THAT FEELS LIKE A FIST IN MY CHEST AND STOMACH...... WHY!!!!!!!! That will last a few hours before it subsides. Also the headaches I m getting from this meds are a doozie I know that s another side effect but my urologist felt this was the best medication for as she put it the nasty UTI that I have. I have IC, Intercycystial cystitis.... Chronic inflammation of the bladder, so at first I thought I had I flare up and by day 4-5, and it hadn t subsided I got into see her....I ve just been so sick with all this I can t take any more....help me please