@clutch - Thanks for the offer. Can you tell me a little about yourself and your experience with this issue? I attribute mine to a family history of constipation and a redundant/tortuous colon (maybe related).
Constipation:
Tried but not particularly helpful - Naturade stool softener laxative, Lactulose (which I found nauseating), Docusate Sodium.
Currently use - Increased water consumption ("float the logs"), high fiber diet from whole plant foods, dried figs or prunes daily , prn use of Miralax (about 3/mo) or Smoothe Move (a Traditional Medicinals tea of senna about 1/month), as health and weather permit - walking as fast as I can 30-40 minutes/day (including stairs) to get my intestines "activated", my uneducated abdominal massage, manually "pulsing" south east of my anus and the dreaded manual extraction (1 year). Very important is keeping a stool shape/frequency diary to take proactive action before things become overwhelming.

I don't get much nausea - when it is felt, it is invariably followed within a few hours by a very satisfying enormous (8-10" long) stool that causes brief jabs of pain as it pushes thru the tortuous colon.
Most of the time, my belly feels "quivery". Sometimes the feeling moves elsewhere, adding to feeling like a shaky old lady.