Stress and anxiety do not CAUSE IBS. If your doctor is telling you that, he is giving you erroneous information.
While the exact CAUSE is not known, it is generally believed that an IBS gut has a heightened sensitivity to the normal function of bowel contractions as well as nervous system complications. Like you, IBS CAUSES my anxiety, not the other way around. However, after living with this condition for over 30 years, I suspect that the two are so closely interwoven that I almost can't separate them anymore. Simply living with a heightened awareness of gut volatility would cause anyone to experience anxiety.
Morning can be stressful for everyone with IBS. For me, it sets the tone for the day. If I have a bad morning, either way (C or D), I can predict how I am going to feel physically for the next 12 hours. Unfortunately, this awareness can become a preoccupation that can limit how one functions in the world. If I know I am going to be in pain and distress for hours, or I fear I may have violent D, I am not going to feel inclined to participate in regular activities. That causes stress, especially if those regular activites include work or child care, etc.