IBS (irritable bowl syndrome) is a diagnosis given when there is a variety of intestinal symptoms, such as cramping, pain, and gas, but the structure of the bowl itself is not abnormal (as it is in diseases such as Crohn's and Ulcerative Colitis.
It is also known as anxious bowel.
In some cases, it has been found that the individual is more sensitive to the sensations of the digestive track. After all, the intestine is nearly constantly active in processing the bodies 'fuel'.
In fact, we now know that there are receptors for Seretonin and endorphins (the body's natural opiates) in the intestinal tract. This is why antidepressants that effect the neurotransmitters Seretonin, as well as opiates slow down the intestinal tract and in some cases provide relief to the symptoms of IBS, although in large amounts they can also cause constipation. Opiates have long been a treatment for diarrhea and irritable bowel (non-addictive derivatives such as Lomotil have replaced the use of opiates in modern times)
So, since you already are aware that you have an issue with anxiety, it is very likely that getting this problem under control will also help your intestinal problems.
Also, it should reassure you to know, that some of the sensations you are aware of are normal, but due to your anxiety may be increased. Worrying more about them can increase the problem.
In anxiety we have an excess of stress hormones released into the system (such as adrenalin and cortisol) this is what gets your heart rate up and also is very much responsible for both constipation and diarrhea that is common in IBS. This is because, when these stress hormones are released, this sends signals to the body to shunt blood flow away from the intestine to the muscles, brain, and cardiovascular system, so that one can prepare to run away from the 'danger' or 'fight'. We developed these chemical responses over the millennium, and our bodies have not developed the ability to tell the difference between a physical threat, and a mental threat (or anxiety). The variation between hyper motility in the intestine, to slow motility is an effect of the release of these neurotransmitters.
So instead of treating the symptoms, I would suggest that you work on treating the core problem. Besides taking medications to decrease anxiety, one can try all the other interventions that are known to help this problem. Cognitive behavioral therapy is very helpful. One of the most helpful interventions, and one you can start immediately is daily exercise. Daily exercise will take up and use the excess stress or anxiety hormones that are released, and you will see an almost immediate decrease in anxiety and should also see a gradual improvement in intestinal symptoms.
Of course it is good that you were evaluated by a physician....you know that you do not have anything serious. The prominent veins occur from straining and constipation. This can improve over time as you get the symptoms of IBS under control.
Diet can still be helpful, as well as taking a fiber supplement to help with regularity and bulk, if needed.
A good article to read further about IBS and treatment, including diet is here:
I hope you find this helpful. Please reply to this post if you do have further questions.