Sounds like you have a food intolerance, do you eat wheat/dairy a lot? Wheat/gluten intolerance can give you the symptoms you describe but so can other foods. Try an elimination diet to see if that helps. You need to be away from gluten for a few weeks to start noticing a difference as it stays in your body for quite some time(15 days) longer in some people.
Not sure of your general diet. Prune juice or Plumsmart is great but you shouldn't need it every day. Need plenty of fiber and fluid. If you tend to eat lots of protein or highly processed foods like white bread, that will slow things down. Also, not sure of your activity level. If you want to move your bowels, you need to move your body. It does help.
I didn't notice any bowel changes when I entered menopause so I don't think that's it. When's the last time you went to your doctor? You should mention this because you may have some kind of problem that is blocking the bowels partially and the pain in the sides, back, nausea and bloating could also be related to ovary problems.
are you drinking at least 1.2 litres of water a day?