Jbug,
The above advice is awesome. But just to make sure, pleae talk to your doc and rule out any physicality first. It is most likely from the meds(I have been there myself many times. It is terrible

) but I also have fibromyalgia and am in perimenopause which can wreak havoc with bowel function.
I find that magnesium, vitamin C and evening primrose oil help me. But sometimes it doesn't. Irritable bowel syndrome for example, can be aggravated by too much fruit or fruit juice or even raw vegetables. I eat a lot of veges but steam them lightly first so they are easier to pass through the bowel but cut down on the fruit. Sucrose in fruit can also be an aggravate. Sucrose in some veges can also do the same. You really need to talk to your doc about how much fibre you need and what else you can do before making any drastic changes to your diet.
Take care,
Michah