Senna tea bag mixed with a litle vitamin c has never failed me to get my bowels going. Good for temporary use but the cramping/stimulatory/ dehydrating effects are not desirable. One way of increasing bowel movements is increasing bile into the colon. Bile salts or coffee enemas/colonics . Saywhatagain hit the nail on the head. Sounds like flora imbalance/shortage in the colon. When there is not enough good bacteria in the colon then there might be a lack of beneficial acids to help push the bowels out. Fiber does not work for people that lack the necessary beneficial bacteria in the colon to convert the fiber to fatty acids which helps to generate Bowel movements.
Lactulose can definetly cause gas. Been there done that. Lactulose is not effective unless a sufficient amount of good bacteria is in the colon. Lactulose did nothing for my bowel movements.