What is the best medicine for making me have a bowel movement?

Start simple, but... Docusate (per pdr) helps moisten & soften hard, dry stools. It is not a true laxative, but facilitates natural defecation, usually within 12 to 72 hours. This is safe & available for anyone over 2, & assumes normal GI anatomy without inflammation, stenosis, extrinsic or instrinsic obstruction. Change in bowels is a "red flag", like weight loss or blood in stool, that needs evaluation if persistent.
Milk of Magnesia (magnesium hydroxide) Milk of magnesia (magnesium hydroxide) is a medicine available over-the-counter which is generally quite safe and effective for relieving constipation. A normal dose for an adult is 2 tablets or 2 tablespoons (30ml) no more than twice a day, and it typically takes anywhere from 30 minutes to 6 hours to take effect. Be sure to drink plenty of water with it, and see a doctor if you're not back to regular within a week.